Because of it hapenning suddenly like you describe, I'd suspect something like the timing belt slipping, or one of the variable intake throttle plates came loose and was swallowed by the engine. What is the timing belt and tensioner history on the vehicle and have you ever inspected the lower intake butterflys?

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