4l80e shifting issues

1991 · Jul 2, 2026

Hi,

I have a 1991 Chevrolet V2500 suburban with a 350 and factory 4l80e. Everything runs and shifts fine but sometimes when I restart the truck, the transmission doesn't shift properly. It stays in first gear for a long time and went harsh into second. That works until 3rd gear. Reverse works fine.

After a couple restarts it works as it should. I'm pretty sure that is an electronic issue but I don't know where to look anymore.

I replaced already

Internal wiring harness 4l80e
TPS sensor
Ignition switch
Map sensor.
Checked all grounds and fuse. I have power coming to the transmission.
Speedometer works fine

Any ideas?

Camar068 · Jul 7, 2026

I've got a 4l60e that I've been expecting to go (no issues as bad as yours). Anyway, I read up on Lubgard and reviews. I felt they were positive enough to add to my transmission. Keep in mind I was the type that would drop the pan change the filter and fluid that came out....and that's it. Anything beyond that, drive it until it goes.

I could tell a difference with torque converter shudder, but shifting is way better than it was before. At least 120k miles on this trans but don't know the real mileage.

Read up on it, with reviews and thoughts from here, then you decide if you want to use it. If "they" say it's on it's way out shortly, it's worth a try.

goldpack · Jul 8, 2026

when was the last time the trans fluid was fully swapped. ?
(just a drain/fill for 50%, or a try for 100% pump through,...what color is it now
fresh cranberry red,...liver blood, brown, black, ...black with flecks).

when was the last time the diff lube was drained/ filled.?

battery fresh/
battery wires fresh (-= looked for corrosion hiding up in the line under the sheath).
= battery problems can be 1st exhibited with trans problems.

1991 · Jul 13, 2026

Thanks for the replies. I'm actually confident that I found the problem. First 4l80e had input and output speed sensors and the connection from my input sensor where pretty dirty. Cleaned it and shifts fine since a couple of days.

Still loosing some ATF through the breather. Temps are fine

4l80e shifting issues

1991

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Camar068

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goldpack

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1991

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