4l80 hard shifting after highway driving- tune?
10-03-2017, 10:42 AM
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4l80 hard shifting after highway driving- tune?
Sorry for the long post but I feel like I need to explain in detail...So I am lost on what my issue is, at this point I am thinking that something in my tune or computer related issue is causing me to eat through 4l80s. I am having issues with my trans shifting hard after some highway driving for about 15-20 minutes. LS swapped 97 GMC K2500 suburban. trans temps are normal, and it does this no matter if they are 190 degrees or 120 degrees. driving at highway speeds constant for a while in 4th and locked up everything is fine, then I will slow down for traffic or construction, then my trans doesnt want to upshift unless i really get into the pedal hard. once it finally shifts weird that time, the rest of the times are fine but it shifts at full line pressure. If I turn the truck off then come back later and go drive every thing is fine then. I saw a post on gm-trucks.com about some guy with very similar issues and it turned out to be his TC slipping on the highway causing his trans to command high line pressure until the truck was off. Using HP tuners I logged tcc slip on the highway locked and it never slipped more than a couple rpm when locked. Since I didnt know what to do I got a used billet converter form a friend and installed that. truck was good for about a day then it didnt want to go into 4th unless the trans was hot, then that got worse and didnt really want to go into 4th at all, even though the computer thought it was in 4th. Then I gave up and got a used 4l80 from the yard with 100k on it, outside was crusty but inside looked in good shape. I left this trans stock along with its stock converter it came with and put it all in. truck ran perfect for a month and now I am having the same highway symptons I first started having months ago. Anyone come across anything like this? could this be a computer issue? I just dont see how I am blowing through these transmissions!!!!
10-03-2017, 08:01 PM
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No trans codes are coming up. The problem with a log is that this doesnt happen every time, and only happens after atleast 10 minutes of driving, so I never really have my computer with me to take a log. for example the last week there hasnt been an issue. I have attached my current tune tough.