4L80-e Trans slips after going into overdrive

[dad375]

I have a 1994 Chev K3500 4wheel drive 454 cu in pickup. The tranny started slipping badly when going into 4th(overdrive). The ECM is throwing no codes. Took it too a tranny shop and they replaced the two solenoids as they stated one was marginal. Did not cure the problem. They had the truck for 10 days(this is a shop with a very good name and has been in business for 50 years) and were unable to determine what was wrong. They think its the PCM which is no longer available from GM. They had a used PCM from an older Chev truck and the problem stopped when they installed it but the speedo was not right. I went to my local Pull-a-Part and pulled two PCMs from 1500s and neither made any difference. The tranny shop did a nationwide search for a used PCM from a truck they same as mine and came up with nothing. We are not sure the PCM is the problem. Has anyone out there had a similar problem and come up with a fix. Thanks for any help you can give.

[j cAT]

Originally Posted by dad375

I have a 1994 Chev K3500 4wheel drive 454 cu in pickup. The tranny started slipping badly when going into 4th(overdrive). The ECM is throwing no codes. Took it too a tranny shop and they replaced the two solenoids as they stated one was marginal. Did not cure the problem. They had the truck for 10 days(this is a shop with a very good name and has been in business for 50 years) and were unable to determine what was wrong. They think its the PCM which is no longer available from GM. They had a used PCM from an older Chev truck and the problem stopped when they installed it but the speedo was not right. I went to my local Pull-a-Part and pulled two PCMs from 1500s and neither made any difference. The tranny shop did a nationwide search for a used PCM from a truck they same as mine and came up with nothing. We are not sure the PCM is the problem. Has anyone out there had a similar problem and come up with a fix. Thanks for any help you can give.

I would go to another tranny shop. this is a common problem . usually the valve bodies wear causing a loss of pressure then it drops out.

solenoids would / could be the problem when they go it is a sudden loss. when its the valve body it gradually gets worse as the pressures drop too low.

if they are really on the ball they would measure the solenoids from the PCM connector ! this old bad wires are a big problem.

[phillipshaw]

maybe you should go to other tranny shop to help you to solve your problem.