Good suggestions. I've ruled out alignment and tire pressure, u-joints, front bearings and all lugs are tight. I don't think it is the trans as it does it while coasting. I dunno if it could be the rear end or carrier bearing. This shakes the whole truck but does not move the steering wheel. I'm thinking of going to pick-a-part and buy a carrier bearing and replace it.

I picked up an engine that is supposed to have good heads on it. They look like cast iron and have a number stamped into them of C8S1A. I don't know if that is a 2.9 for sure. The only number I could find was 86TM when I did a search.