dodge trans shift problems

what would cause a auto trans to shift up and down when moving at 65 mph also the truck idles at a surge of 500 to 1250 rpm when parked this is a dodge 1997 2500 hd with 360 ci

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Probably going in and out of overdrive. Idle could be a tps.
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Yep - both problems sound TPS-related. The TPS will cause the trans to lock/unlock (it's probably the converter locking/unlocking, not actually shifting between 3 and 4), and will also cause the computer to chase the idle... TPS spikes to a higher voltage, and the PCM immediately increases the amount of fuel, anticipating more air. But, since the throttle plates haven't really moved, the idle goes rich, dropping the RPMs, then the PCM cuts the fuel, going lean, bringing the RPMs up. Lather, rinse, repeat.
To the OP: the Throttle Position Sensor is bolted to the side of the throttle body, underneath the air intake. It's the sensor on the opposite side of the throttle cable linkage. Do you know how to back-probe an electrical device, and check it's voltage output (preferably with an analog multi-meter)? If so, you can diagnose the sensor yourself pretty easily. If not, you could have a shop do it, or you could gamble the $40-or-so for a new part, and swap it out, hoping that it's really the problem.
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Or torque converter lockup/unlockup?
On GMs (Yea, I've got a few of them too...) the TPS will account for both problems. Not sure about Dodge however.
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