I work in a salvage yard & REFUSE to sell an exploder transmission. It's just plain junk. Not designed for the HP & weight of the vehicle.

If you insist, get a FULL rebuild from a reputable shop.

We gave up selling those transmissions after pulling 4 to get 1 good one, even though we tested them before pulling them. Line pressures were in spec.

I would go for the 4.3 swap, as the engine/trans is much healthier & you can find a donor for it cheap.

2.8 would be a waste in my opinion, but the 2.5 5speed & 3.4L might be a go. Just change the head gaskets, as they have issues. Also, before installing any engine, swap out the seals & water pump.

Good luck...

Ed