There were 2 different ECMs available for 1985:
1226455:
6000 84 Elec Cont Module (ECM); 6-173 (2.8L)
BLAZER S10/JIMMY S15 84 Elec Cont Module (ECM); (6-173, 2.8L)
BLAZER/JIMMY (full size) 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226455
BONNEVILLE 84 Elec Cont Module (ECM); 8-305 (5.0L)
CAMARO 84 Elec Cont Module (ECM); 6-173 (2.8L)
CAMARO 84 Elec Cont Module (ECM); 8-305 (5.0L)
CAPRICE 84 Elec Cont Module (ECM); 8-305 (5.0L)
CAPRICE 84 Elec Cont Module (ECM); 8-350 (5.7L, gasoline)
CELEBRITY 84 Elec Cont Module (ECM); 6-173 (2.8L)
CENTURY 84 Elec Cont Module (ECM); 6-173 (2.8L)
CHEVROLET FORWARD CONTROL 84 Elec Cont Module (ECM); 8-350 (5.7L)
CHEVROLET FORWARD CONTROL 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226455
CHEVROLET VAN 84 Elec Cont Module (ECM); 8-305 (5.0L)
CHEVROLET VAN 84 Elec Cont Module (ECM); 8-350 (5.7L)
CHEVROLET VAN 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226455
CHEVROLET 10 PICKUP 84 Elec Cont Module (ECM); 8-305 (5.0L)
CHEVROLET 10 PICKUP 84 Elec Cont Module (ECM); 8-350 (5.7L)
CHEVROLET 10 PICKUP 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226455
CHEVROLET 20 PICKUP 84 Elec Cont Module (ECM); 8-305 (5.0L)
CHEVROLET 20 PICKUP 84 Elec Cont Module (ECM); 8-350 (5.7L)
CHEVROLET 20 PICKUP 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226455
CHEVROLET 30 PICKUP 84 Elec Cont Module (ECM); 8-350 (5.7L)
CHEVROLET 30 PICKUP 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226455
CIERA 84 Elec Cont Module (ECM); 6-173 (2.8L)
CITATION 84 Elec Cont Module (ECM); 6-173 (2.8L)
FIREBIRD 84 Elec Cont Module (ECM); 6-173 (2.8L)
FIREBIRD 84 Elec Cont Module (ECM); 8-305 (5.0L)
GMC 1500 PICKUP 84 Elec Cont Module (ECM); 8-305 (5.0L)
GMC 1500 PICKUP 84 Elec Cont Module (ECM); 8-350 (5.7L)
GMC 1500 PICKUP 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226455
GMC 2500 PICKUP 84 Elec Cont Module (ECM); 8-305 (5.0L)
GMC 2500 PICKUP 84 Elec Cont Module (ECM); 8-350 (5.7L)
GMC 2500 PICKUP 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226455
GMC 3500 PICKUP 84 Elec Cont Module (ECM); 8-350 (5.7L)
GMC 3500 PICKUP 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226455
GMC FORWARD CONTROL 84 Elec Cont Module (ECM); 8-350 (5.7L)
GMC FORWARD CONTROL 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226455
GMC VAN 84 Elec Cont Module (ECM); 8-305 (5.0L)
GMC VAN 84 Elec Cont Module (ECM); 8-350 (5.7L)
GMC VAN 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226455
GRAND PRIX 84 Elec Cont Module (ECM); 8-305 (5.0L)
IMPALA 84 Elec Cont Module (ECM); 8-305 (5.0L)
IMPALA 84 Elec Cont Module (ECM); 8-350 (5.7L, gasoline)
MALIBU 84 Elec Cont Module (ECM); 8-305 (5.0L)
MONTE CARLO 84 Elec Cont Module (ECM); 8-305 (5.0L)
OMEGA 84 Elec Cont Module (ECM); 6-173 (2.8L)
PARISIENNE 84 Elec Cont Module (ECM); 8-305 (5.0L)
PHOENIX 84 Elec Cont Module (ECM); 6-173 (2.8L)
S10/S15/SONOMA 84 Elec Cont Module (ECM); (6-173, 2.8L)
SKYLARK 84 Elec Cont Module (ECM); 6-173 (2.8L)
SPRINT (GMC) 84 Elec Cont Module (ECM); 8-305 (5.0L)
SUBURBAN 10 84 Elec Cont Module (ECM); 8-305 (5.0L)
SUBURBAN 10 84 Elec Cont Module (ECM); 8-350 (5.7L)
SUBURBAN 10 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226455
SUBURBAN 1500 84 Elec Cont Module (ECM); 8-305 (5.0L)
SUBURBAN 1500 84 Elec Cont Module (ECM); 8-350 (5.7L)
SUBURBAN 1500 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226455
SUBURBAN 20 84 Elec Cont Module (ECM); 8-350 (5.7L)
SUBURBAN 20 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226455
SUBURBAN 2500 84 Elec Cont Module (ECM); 8-350 (5.7L)
SUBURBAN 2500 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226455
And 1226865
6000 85-86 Elec Cont Module (ECM); 6-173 (2.8L), 2BC
ASTRO 85 Elec Cont Module (ECM); 6-262 (4.3L)
BLAZER S10/JIMMY S15 85 Elec Cont Module (ECM); 6-173 (2.8L)
BLAZER/JIMMY (full size) 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226865
BLAZER/JIMMY (full size) 85-86 Elec Cont Module (ECM); 8-305 (5.0L)
BLAZER/JIMMY (full size) 86 Elec Cont Module (ECM); 8-350 (5.7L)
BONNEVILLE 85 Elec Cont Module (ECM); 8-305 (5.0L)
CAMARO 85 Elec Cont Module (ECM); 8-305 (5.0L), 4BC
CAPRICE 85 Elec Cont Module (ECM); 8-305 (5.0L)
CAPRICE 85 Elec Cont Module (ECM); 8-350 (5.7L), gasoline
CELEBRITY 85-86 Elec Cont Module (ECM); 6-173 (2.8L), 2BC
CENTURY 85 Elec Cont Module (ECM); 6-173 (2.8L), 2BC
CENTURY 86 Elec Cont Module (ECM); 6-173 (2.8L)
CHEVROLET FORWARD CONTROL 85 Elec Cont Module (ECM); 6-262 (4.3L)
CHEVROLET FORWARD CONTROL 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226865
CHEVROLET FORWARD CONTROL 86 Elec Cont Module (ECM)
CHEVROLET VAN 85 Elec Cont Module (ECM); 6-262 (4.3L)
CHEVROLET VAN 85 Elec Cont Module (ECM); 8-305 (5.0L)
CHEVROLET VAN 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226865
CHEVROLET VAN 86 Elec Cont Module (ECM)
CHEVROLET 10 PICKUP 85 Elec Cont Module (ECM); 6-262 (4.3L)
CHEVROLET 10 PICKUP 85 Elec Cont Module (ECM); 8-305 (5.0L)
CHEVROLET 10 PICKUP 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226865
CHEVROLET 10 PICKUP 86 Elec Cont Module (ECM); (behind glovebox)
CHEVROLET 20 PICKUP 85 Elec Cont Module (ECM); 6-262 (4.3L)
CHEVROLET 20 PICKUP 85 Elec Cont Module (ECM); 8-305 (5.0L)
CHEVROLET 20 PICKUP 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226865
CHEVROLET 20 PICKUP 86 Elec Cont Module (ECM)
CHEVROLET 30 PICKUP 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226865
CHEVROLET 30 PICKUP 86 Elec Cont Module (ECM)
CIERA 85 Elec Cont Module (ECM); 6-173 (2.8L), 2BC
CIERA 86 Elec Cont Module (ECM); 6-173 (2.8L), VIN (8th digit) "X"
CITATION 85 Elec Cont Module (ECM); 6-173 (2.8L), VIN (8th digit) "X"
CUTLASS 86 Elec Cont Module (ECM); 6-173 (2.8L), VIN (8th digit) "X"
FIREBIRD 85 Elec Cont Module (ECM); 8-305 (5.0L), 4BC
GMC 1500 PICKUP 85 Elec Cont Module (ECM); 6-262 (4.3L)
GMC 1500 PICKUP 85 Elec Cont Module (ECM); 8-305 (5.0L)
GMC 1500 PICKUP 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226865
GMC 1500 PICKUP 86 Elec Cont Module (ECM); (behind glovebox)
GMC 2500 PICKUP 85 Elec Cont Module (ECM); 6-262 (4.3L)
GMC 2500 PICKUP 85 Elec Cont Module (ECM); 8-305 (5.0L)
GMC 2500 PICKUP 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226865
GMC 2500 PICKUP 86 Elec Cont Module (ECM)
GMC 3500 PICKUP 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226865
GMC 3500 PICKUP 86 Elec Cont Module (ECM)
GMC FORWARD CONTROL 85 Elec Cont Module (ECM); 6-262 (4.3L)
GMC FORWARD CONTROL 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226865
GMC FORWARD CONTROL 86 Elec Cont Module (ECM)
GMC VAN 85 Elec Cont Module (ECM); 6-262 (4.3L)
GMC VAN 85 Elec Cont Module (ECM); 8-305 (5.0L)
GMC VAN 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226865
GMC VAN 86 Elec Cont Module (ECM)
GRAND PRIX 85 Elec Cont Module (ECM); 8-305 (5.0L)
IMPALA 85 Elec Cont Module (ECM); 8-305 (5.0L)
IMPALA 85 Elec Cont Module (ECM); 8-350 (5.7L), gasoline
MALIBU 85 Elec Cont Module (ECM); 8-305 (5.0L)
MONTE CARLO 85 Elec Cont Module (ECM); 8-305 (5.0L)
PARISIENNE 85 Elec Cont Module (ECM); 8-305 (5.0L)
S10/S15/SONOMA 85 Elec Cont Module (ECM); 6-173 (2.8L)
SAFARI (GMC) 85 Elec Cont Module (ECM); 6-262 (4.3L)
SKYLARK 85 Elec Cont Module (ECM); 6-173 (2.8L), 2BC
SPRINT (GMC) 85 Elec Cont Module (ECM); 8-305 (5.0L)
SUBURBAN 10 85 Elec Cont Module (ECM); 8-305 (5.0L)
SUBURBAN 10 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226865
SUBURBAN 10 86 Elec Cont Module (ECM)
SUBURBAN 1500 85 Elec Cont Module (ECM); 8-305 (5.0L)
SUBURBAN 1500 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226865
SUBURBAN 1500 86 Elec Cont Module (ECM)
SUBURBAN 20 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226865
SUBURBAN 20 86 Elec Cont Module (ECM)
SUBURBAN 2500 85 Elec Cont Module (ECM); 8-350 (5.7L), ID 1226865
SUBURBAN 2500 86 Elec Cont Module (ECM)
I'm assuming you need 6865 since it's only available in 1986.