On a trip back from KY my '97 started acting up and would intermittently lose acceleration. The engine would rev like it was in neutral or park and none of the gears would engage. After shutting it off and starting it back up it was once again able to be driven.

I made it back, went a move and a few other things, then finally tackled everything. I did a fluid and filter change, but the same issue. Actually it got worse after that and I snagged a lower mileage trans from a donor I bought (drove perfectly fine) and swapped it in. It seemed to drive fine and then the issue came back. The only thing I reused off my original D1 was the torque converter because I had promised the other to a friend who needed it.

Now my truck will drive fine for awhile, but there is a slight thump no matter what gear is selected while it's at idle and it will randomly lose drive. I'm leaning towards this being the torque converter and possibly the flex plate? It looked perfectly fine when I had the trans out before.

TLDR
Was an idiot and reused my old torque converter possibly causing me to pull it all again.