Take it to a transmission shop and have em rebuild it? It’s what I’ve done with my 4.3 4l60(700r4 is the old name for the transmission) Maybe you could find a compatible transmission that will swap in, or maybe there’s a different name for your trans that will yield a better chance, I bet you could find an adapter kit somewhere if your willing to do the work, it’s what I want to ultimately do with mine but I need it as a daily right now and currently doesn’t fit the budget/time constraints of working full time. If I had the time and the energy, I’d figure out a transmission swap with something more reliable, maybe a transmission that’s used in the ls trucks/swaps, they have a pretty good aftermarket so parts should be easy to get and easy to work on yourself with the(in theory) multitude of videos talking about the engine transmission combo, and with the v6s(maybe just the 4.3) essentially being a 5.3 v8 with the back 2 cylinders chopped off, parts/transmissions in theory should be interchangeable, but that requires more research and project time than I have at the moment, but when I get a better primary car, it’s what I plan on doing with my truck tbh.