I've had them jump anywhere from 2-5 teeth and you can notice the difference. Once on top everything seems to be running smooth but it will idle like shit. You can connect a datalogger and watch/record your timing advance. Thats one way to figure it out. Timing might be fine up top but I would check the crankshaft sprocket as well.

Could be a timing issue like it was mentioned. Did you buy a OEM Mitsubishi replacement belt (Dealer or dealer source). Or did you buy a supposely OEM spec aftermarket belt? Usually aftermarket belts tend to stretch and will jump teeth. I have had this happen to me twice in previous 1g's with 6 bolts in them.