Mitsubishi Repair: 1990 Montero 3.0L, throttle position sensor, timing belts

Question
I have a 3.0L Montero that just started hesitating during acceleration.  At about 1/4 throttle it runs fine, accelerates fine, but any more throttle feels like the timing is retarded.  Does not matter if under load (driving or stopped)  It almost feels like the spark is cut off, but it misfires a little.  I looked at all of the vacuum hoses, all look fine.  New ECM 1 year ago, fuel pump 6 months ago.  Could it be the throttle position sensor?   A local shop said to check the timing belts, which I have not done yet.  Have you run across this problem in the past?

Answer
Shane: I agree with the shop, I would checking those timing belts, if one of those goes you could loose the engine. So best do that next.  You could code the computer too, it would let you know what going on also.You did get the right computer for the car, model, year and make right? A new one, you didn't go out to the junk yard and buy one off a old car? Ok, I am hoping you bought a new computer, some people will get old one out of older cars and then it messes up their cars. So just checking. God bless: Linda