How many miles you got on that rig anyway? Also, what was the motivation for doing $5500 worth of engine work? Was there an existing problem or preventative maintenance? Doesn't make any sense to me to do all that engine work and leave out the most common reason why these rigs need engine work in the first place (valve guide seals). Your engine guy should have known this.

Better plan on another $1K to fix your current problem.

1991 Montero LS, fading red paint
Front and rear limited slip differentials
95 SR Rear Springs, torsion bar crank, 137,650 miles
33x12.5 ProComp Mud Terrains, Bushwacker Fender flares
3 litre V6 with new heads