1994 GMC Suburban Transmission problems

MASTERPLUMBERPA

MEMBER
1994 GMC

Hello, I have a 1994 GMC Suburban with 190,000 miles on the 5.7L engine w/automatic trans. It has been well maintained but I'm having a few problems. The first is with the transmission. Basically, it will not shift automatically from 1st to 2nd. The RPM will actually redline if you stay on the gas. When I take off of the gas at higher RPM's and then press it again, it will shift into 2nd gear. No problem with shifting from 2nd to 3rd, etc. The truck doesn't have any acceleration problems and when I treat it like a manual by taking off gas & pressing again, it's pretty much all good. Any suggestions or has anyone had a similar problem?
The second issue is since I bought the truck used @ 4 years ago the oil pressure gauge never reads normal, always very low once warmed up a little. No knocking or any other problem with acceleration etc. It just has me concerned. Oil/filter changed regularly and a once or twice I even did an oil flush on it when changing the oil. Nothing changes, remaines an issue. Any suggestions on this?

2 Replies

AACPLUS

MEMBER
60 POSTS

If it's a 4L60E, I would have the solenoids tested. This does not require removal, just the valve body for R & R. The solenoids can be tested through the electronic harness plug. (Top right) with break out box or get a diagram. Check for correct ohms.

The 4L60E is notorious for problems. That is probably why it has been re-designed a few times, as well as the fluid. Mercon II, Mercon III, mercon IV.

If it is a THM400, could be a vacuum problem. Modulator or a vacuum leak.