If there is much wear in the throttle shaft bushing, the slop will cause the TPS wiper contact to be off center. Check your reference voltage just to eliminate that as a possible cause. That's all I can think of. My 2000 TJ 2.5 has 150k plus on it and still running the one from when she was new.I have an 04 tj. It's a 4 cyl and in the past year I have had it the throttle position sensor has gone out on it 3 times. So I'm guessing there is an underlying problem there. Any ideas anyone?