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Transmission works okay when cold, but loses reverse when warm. Sometimes goes into limp mode 2nd gear only but works again after cooling down. 1994 heavy 3/4 ton 4x4 with the 454 engine.  

Any ideas?  

My guess would be a bad center support and direct drum. That is what usually goes bad on those trannys. The direct drum {3rd and reverse} sits on top of the center support and gets hydraulic pressure through those sealing rings. Those two parts get worn out right where they seal together. When the computer senses a slip in 3rd it puts the trans in limp mode . Have the computer scanned and post the codes here.  

I agree with 440t4 (he's a smart cookie), if the clutches are not burned too bad, you can put in a Transgo Shift Kit..which is not difficult to do and works "miracles" on the 4L80E.  But please take note, IF the clutches and/or drum or center support is bad...that miracle will not help, you will have to go and have it rebuilt.  

I will try to get it in soon to be scanned. I wouldnt think the clutches are worn to bad since it works fine cold other than slow shifts, but then I'm not an expert either. I have been wrong before. So what do you think my chances are that a shift kit will fix it?  

If a simple fix wont cure it then I dont want to spend anymore money on parts, I will just take it in for a rebuild. I'll get it scanned first and listen to your suggestions.  

Redhawke
Despite the fact that all of the transmission shops around here said it would never work, I installed the Transgo HD2 shift kit and my troubles are over! My transmission works better than ever. Thank you for saving me hundreds of dollars. I definitely did not have hundreds to spare.