Mine has no problems with extended RPM's, it'll spin 4500 to 5000 with out loss of oil pressure or the temp climbing. When we were pulling my Snow mobiles up the mountain couple of weeks ago we had no problems running running that RPM to keep from shifting to 3rd and bogging down, for about 15 min. total and nothing was hurt except fuel mileage. BTW I have a 2.6L- 3.5 has great torque, as long as your below redline you should be fine and only use High rpm's when you absolutly have to, I dont like to run High RPM's unless I have to.

89'Isuzu Trooper LS 5 spd 2.6L
31" Big O X/T's
15x8 Eagle 058's
K&N Filter w/ Air Box Mod
2.25" DynoMax SuperTurbo
PolyUrathane/Indy4X Bushings
Suspension/ FrontEnd Tech/Hunter Certified Alignment Tech.