Hello!! Help please

[Mjackson4120]

So I have a 93 Chevy suburban 2500 4x4 454 motor 4l80e trans.
Problem no overdrive on the highway. I have replaced solenoids for gears 2&3 and the tcc solenoid changed filter but not fluid. Replaced the brake switch on the brake pedal and the tps sensor which had to be modified to sit right so the the engine would idle normally. All other gears are fine shifts perfectly with plenty of power just can't get that last lock up to stay. It will go into the last gear but only for a couple of min. Any ideas.also can't seem to find it anywhere what should be the idle rpm for that motor?

 

[ak diesel driver]

is it 4th gear or the TCC?

 

[Mjackson4120]

To me when driving it only feels like 4 gears. So she goes through 123 just fine. I just changed the fluid and she seemed to hold in that last highway gear for a little longer but then it's lile you hit the gas goes into passing gear and then wont go back into that highway cruising gear I hope that makes sense. Could it be the pressure control solenoid? I mean she drives like a top other than not staying in that gear

 

[Mjackson4120]

Or do I need to be looking at electrical I have read alot about the wiring harnesses on the 4l80e going bad and needing to replace it and the outside pigtail with a updated harness

 

[ak diesel driver]

alot of people mistake TCC lockup for a gear, count carefully. Helps to know what is actually happening

 

[ak diesel driver]

also the TCC will lock in 3rd gear as well assuming you are over the speed threshold (usually around 50) and don't have alot of throttle input

 

[THEFERMANATOR]

Getting a scanner on it or paying somebody to check it is alot cheaper than throwing parts at it. And new parts does not mean good parts. I couldnt tell you how many times I've seen somebody throw bad new parts at a problem only to make it worse. This isnt the kind of problem to guess at, you need to see what the ecm is seeing, and why its doing or not doing what it should be.