i am on my 4th trooper. i had one w/ an efi 2.8 v6, a carbed 2.3 I4, an efi 2.6 I4, and now an efi 3.4 v6 (upgraded from 2.8). the 2.8 is a dog with anything over a 31" tire. the 2.3 and 2.6, to me, seem to have more torque down low.
the 3.4 takes the cake though. more power all over the place.
what I am getting at is, if you want a lot of power, get a 2.8 troop and swap in the 3.4 from a camaro (almost a direct bolt in, all 2.8 junk bolts on. caddy, olds, and other gm engines will also "bolt" to the trans, but will take more work w/ fuel delivery, electircal system etc).
if you dont want to mess with swapping an engine, a 2.6 will work fine. BUT if you don't have tiny little double-jointed hands, everytime you have to work on the 2.6, you will curse the sadistic engineers who designed the fawker.
if you don't care about power at all, and could use something that gets pretty decent mpg, the 2.3 is great. torquey, easy to work on, and i got 20-25 mpg. only problem with those troopers (86-87) is that they have smaller, weaker diffs. but they have the cool round headlights.
aftermarket includes tera 3:1 low range, 5.38 diff gears, arb, a few limited slip, lockright. auto hubs aren't up to abuse, but aisin stock manual hubs are great, warn and superwinch also make some.
the best thing about them is that are a great platform for a dd or trail rig (or both).
4x4wire.com has a big isuzu section with just about everything you'd want to know.