I have a 86 fourwheel drive cherokee with a 3" lift that has severe bumpsteer after fortyfive mph. I have adjusted the caster and fixed it the first time but I took a trailride and now have bumpsteer again.

Check your tie rod ends, and steering damper. Also do a search on here for death wobble which is what it's more commonly known as.

Also consider a local or slightly, but safely commuted 4x4 shop. Drop pitman arm for 3"??

I was on the highway once with a fella that had the DW's BAAAD!!! He scared me from 2 lanes over! Be Careful. GET IT FIXED!

You don't usually need a drop pitman arm until you get to 4-5 inches and higher because at 3 inches and less the angles on the linkage isn't to bad. Once you seem to hit the 4-5 mark is when it starts getting worse. At 3 inches and them being gone after alignment and then coming back after a trail ride I'd say prolly balljoint or tre, also don't forget to check the ends of the drag link as one of them could be worn out causing it.