94 suburban SLE 454, tranny not shifting.?

Can't edit my answer to details....

Original incident was Thanksgiving. I was going downhill and suddenly was over revving when the hill ended. Just happened out of nowhere.

After cool down it worked normally again.

Today's incident happened as I got on freeway.

Took it to get food after it cooled, everything back to normal again.

It's some sort of intermittent problem.

Vehicle is a 94 k2500 GMC suburban. Pretty much fully loaded. 454 motor.

Haven't had a chance to look under it at the pan, but thanks to the guy who said what to look for.

And original incident happened right after I put a hotter winter time thermostat in it.

I've only owned the vehicle since July. I got it for 500 as a mechanics special with blown head gaskets.

I don't think the higher running temp makes any difference, or I would of had a problem back in July before junking the 195 thermostat for a 160.

Current thermostat is 180.

Is there some wiring I should look at, or just solenoids?

actually the suburban used both the 4L60E and the 4L80E in that year depending on engine. the 60 would have a square pan the 80 will be rounded off in the back. both have shift solenoids usually a check engine light would be on if one of them would be bad. if fluid checks O.K I'm leaning towards one of the solenoids. the 80 series had the solenoids updated a couple of times over the years. but either way replace both solenoids on whichever transmission you have both located on the valve body. the 60 solenoids are held in place with clips. hold the solenoids in place since the 1-2 shift solenoid is spring loaded. the 80 solenoids are bolted in place with a 27 torx bit/ before buying them pull pan then see how much material is in the pan if a lot suspect a internal problem. if it looks good then try the solenoids

tranny needs to be torn down and problem discovered. stuck in second seems like something inside is broken -- could be the selector/shifter gear, could be a broken gear tooth has lodged somewhere that prevents shifter from working.

and do NOT run the vehicle up to the red line in second gear. You can maybe get it to a service guy without ruining anything -- but keep speed down under 35.

[yes, i know it has no power -- that's because it can't shift down into first.]

Pull the main electrical plug on the side of the transmission and look for issues especially fluid. Those early E transmissions had issues with fluid leaks into the connector which then caused all sorts of issues. I believe there was an updated socket that could be installed. There may also be updates to the internal solenoids.

Possible vacuum leak at the MAP sensor not allowing torque converter lock up.Check the vacuum line from the map sensor to the throttle body for broken line.The trans will not shift properly if you have a vacuum leak.

This is my suggestion. DO NOT take it to a place like AAMCO. They are a transmission store, and have a huge markup on parts. Find an automatic transmission shop that is ATRA certified.

http://www.atra.com/shopfinder

The tranny is SHOT - no quick fixes for this one.