The first thing I'd be looking at is the maintenance history - when were the plugs, wires, cap, rotor, oil & oil filter, fuel filter, and air filter last replaced? Is the ignition timing set properly? Are the tires properly inflated? If all of the above have been addressed, then you would start looking at more unusual causes - coolant temp sensor, dragging brakes, transmission or transfer case issues, sticking distributor advance, clogged catalytic converter, etc.

95 Montero SR
3.8 MIVEC, Advance headers, 2 1/2" exhaust, Magnaflow muffler, OME shocks & rear springs, 2" body lift, 3" tank lift, 4.90s, TRE front locker, factory rear locker, Roger Brown Rock Sliderz, 315/75r16 (35") tires, Sport big brakes