Yours sits just like mine with OME 910s <img src="/forums/images/graemlins/lol.gif" alt="" />. I just picked up some gen 2 upper contol arms to correct that some day.
A slow speed sounds like a wieght lost or a tire with a broken belt.
I just put one joint in the frt. of the rear shaft and had it balanced. Cost $115 labor here in Kaliforny , which aint bad at all for here.
I have a little play in the output shaft of the T-case that I beleive contributes to vibe. I had the bushing in the T-case R output made and pressed in by "Omega Machine" in Sacramento <img src="/forums/images/graemlins/kewl.gif" alt="" />.
U joints on these need to have the right thickness in the c clips for good balance.
Koyo joints are the best by far , but Mitsu doesn't sell parts for our vehicles anymore so I went with Precesion brand from napa.
Good luck...

dave h.
'89 Raider V6 5spd;Aisin Hubs;; Gen2 LS: frt. brakes, rear coils;U.C.arms;R.trailing arms;idler arm; rear LSD axle w.disc brakes ;2 battery system for Dog's fan; relocated ECU; custom bumpers;J.Baker receiver;Conferr roofrack; t-bar crank.