Heres a thought. The Wife's trooper has the 3.5L in it.(supposedly second one) What bell housing bolt pattern do these use? A nice MPFI 4.3L would probably be a great swap.
Sorry if its been done a million times, I'm new to the Isuzu world.
I don't think the 4.3 will bolt to the 3.5 and the electronics could be a problem but really the 3.5 twin cam engine is a strong performer when serviced right (215HP from 213 Cubic In.) I use Shell Rotella T 15-40 Wt. changed on a regular bases and it uses no oil and runs very strong. Dave