Couple options:
1. there's 1 company that has commonly reprogrammed obd1 PCMs. They are B&G performance. Not the greatest results though. Their work is really more of a guess as every engine is different and it takes dialing in to really get it there. This is complicated for obd1 because you have to repeatedly send in the PCM and even then, without any kind of datalogging you're guessing.
2. You can convert to OBD2. Kind of a pain, probably better off with buying a 96+ truck in the first place. If you wish to convert, a 96 or 97 parts truck is your best place to start.
3. Mopar Performance PCM. Mopar produced an aftermarket PCM with more aggressive timing and fuel maps. Requires higher octane which means if you're in an area where it can be hard to find you can't change the program to match available fuels. With my truck's SCT tune and my car's Motoza tune for example, I have to run 91 as there's no 93 available. 1 station in a 1hour circle of me and it's Walmart lol. No thx
4. Standalone engine management like Holley or others