I have a 6.0 in my 88 suburban with a 4l80e behind it. When I am going down the highway it won't shift into overdrive most of the time and its running 3k rpm in third gear at 65 or so. Sometimes it will go into overdrive but it slams hard into overdrive like it has a stage three shift kit or something and it stock. Also in when I have the shifter in drive or overdrive it will surge in between second and third like it can't decide which gear to be in. If I put the shifter in second it does fine in second and first but it shifts out of first at like 5mph doesn't even rev very high before it shifts unless you shift it manually. It pulls real good in each gear if you can get it there. Its been like this the whole time since I have put it in. I am thinking electroincs but not sure any help or opinions are greatly appreciated.

 

What year 4L80E? Do you have any codes? PM me your email address and I can send you some information on 4L80E transmisions. I've learned alot about them this summer after having some problems with the one I put in my 81 trans am.

 

did the computer match the trans, and the engine-almost sounds like the throttle postion sensor-they changed the force motor around 93, and the computer has to match

 

yeah its the tranny that was atached to the motor from the Factory. I looked at the truck the day they broiught it in. Its an 07 classic body style. The computer and everything matches. I just took it out to see if I had done some wiring wrong cause I had the lockup hooked where it never unlocked but I fixed that and it still did the same thing. It did good when the tranny fluid was cold but when It gets warmed up it does it way worse, its real subtle when the fluid is cold but real noticable when its warm.