Transmission not shifting into overdrive?

I would do a trans service, fluid and filter. Make sure that you use the right fluid. Atf + 4. Also dis-connect the battery for a few minutes. Remove the positive first and put it back on last, this will allow the vehicle to relearn it's shift patterns.

Have this scanned for codes. It may be more than what you are trying to do.

It sound like the overdrive control solenoid has gone out. Here is a guide and some diagram (Below) to help you get the the problem fixed.

https://www.2carpros.com/articles/how-to-service-an-automatic-transmission

Also, I need you to check something. Get in the truck and place the key in the ignition. Cycle the key from off to the run position 3 times (do not start engine). On the 3rd time, let the key stay in the run position. The check engine light will begin to flash codes.

The codes for a 92 are 2 digit numbers. The light will flash then there will be a sligh pause and it will start again to identify the 2nd number of the code. After it finishes the code, there will be a longer pause and it will move on to the next.

Count the flashes to keep track of the codes. Let me know if there are any and what they are if you find any.

I got you beat (but not by much), my 92 has 220K on it and going strong. It has a 5 speed which will outlast the truck. I use it to haul, plow snow, tow a motorcycle trailer... I love it. We'll figure your problem out. Just hang in there.

At this point, something tells me the torque converter isn't locking up to give you OD, but the backfiring and missing has added a new problem.

Let me know about the code. Also, when you get to code 55, that indicates it has finished.

Let me know what happens

Cheers, Joe

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Cheers, Joe

Has the check engine light come on? Is the trans fluid clean and full?

You need to have the trans control module scanned to see if there are any codes. It could be caused by a few different things. None of which are cheap enough to just throw money away.