all seems to be well, except it won't downshift when you stomp the gas pedal, the engine revs high but that is it. Is this a linkage adjustment problem, speed sensor problem, or what? No service engine light, or anything. I would never have known anything was wrong except for starting to pass in a hurry and it not downshifting into overdrive.
Changed fluid and filter with no help there.
Any ideas????

 

I had the same issue on same model year...I have the 5.7Vortec engine.....mine was a faulty fuel pump, which is located in the tank. Is your fuel pump seem louder than usual? Mine got really loud, I could hear it inside the cab at an idle when I started getting the "no downshift" problems.

Good luck

 

Sounds like the same problem I had with my 88 Silverado shortly after replacing the transmission. After I took the tank down I found the plastic clamp at the pump came loose and might have caused the fuel not to go in the line properly or just wasn't putting out enough pressure. After I changed the pump, that truck hauled *** like never before. I probably would have kept it if it wasn't already sold. It had the problem when the new owner was driving it home. Luckly he lived less than 10 minutes away.

 

1998 Silverado stays in 3rd won't shift to overdrive would it be the speed sensor? if so where is it located? This is a used trans that replaced the original 1998 4l65e.
It seems like first and second is the same and third works but in overdrive it seems like still in third gear.