I have a 1986 K20 with a crate engine with fewer than 5k miles. 350/TH400, 4:10 gears, Edelbrock 1406 carburetor. Truck runs fine, Starts fine. Stops fine. Carb is not that old and I tried a brand new one. All I get is 10 MPG, no matter what. New plugs, new wires. Timing is about 10 degrees...