I have a 4.3 V6 in my Astro, tow a 4500lb travel trailer with it. The van is around 4000lbs itself. I would assume a full size truck weighs more? I would not put more weight than that behind my van, and if the trans does not have a cooler, I would highly recommend one. The engine/trans have been reliable, not so much for the rest of the van. Those motors can go 300-400k if taken care of. The '92 version of the 4.3 likely still has throttle body injection, so less hp than the Vortec engine that I have. My van has 3.42 gears. Check the gears in that truck, that will make a world of difference.