4.0 is diff-
Well as has been alluded to, do the standard tests to see the overall condition: Leak down/compression test to determine piston rings/bore and valve sealing condition, as well as make an accurate assessment of the oil pressure when hot as an indicator of bearing/journal wear.
If those parameters are within specs look in other areas- tune up, injectors, vac leaks. The Trooper engine was due for replacement or big repair, not normally the 4.0. Completely different animal.