9370 troubles

Hello everyone first post here been lurking / searching for a while here.

I have a 1986 International 9370 that was a tandem axle double framed truck. I bought it removed about 2ft of length and made it a single axle. I put a service body on it for my welding company. My problem is a hop in what feels like the front end of the truck. I feel it in the seat and it generally makes the whole cab bounce. When I went from tandem to single I reused wedges from the front rear in the rear rear to get correct pinion angle. Driveshaft is new from transmission output yoke clear to differential input yoke.
I have rebushed rear axle control arms (I have z leaf air ride) replaced drive tires. Shocks front and rear. Had king pins done, converted steer axle from dayton spoke to hub pilot. Nothing has seemed to change the problem. I installed new steer tires this week and used beads to balance them. I thought that fixed it but now intermittently it will come back. Generally happens at around 35-50mph goes away and comes back sometimes at 70+ .

I have raised and lowered ride height with no change, driveline shop suggested dropping carried bearing which didn't help. I pulled drain plug in the rear axle to see if I had brass in oil and I didn't. Rear oil only has a few thousand miles on it. On my list of things to do is front spring bushings and sometime transmission mount bushings. I don't ever feel it in the steering wheel or the gear shifter. Seems to only bounce the truck and not all the time. Certain highway surfaces will give me the same affect such as concrete sections of roads leads me to think maybe it's a suspension issue which hopefully bushings would correct.

Anyway sorry for the long post and I did search before posting just didn't seem to find my answer. Does anyone have any advice?

Thanks so much! Jeremy