transmission down shifting

2000 hummer transmission down shifts on its own any ideas
are there any computors controlling trans?

Check your TPS (throttle position sensor)

2000 hummer transmission down shifts on its own any ideas
are there any computors controlling trans?

The Transmission Control Module receives feedback from the TPS and the Engine Speed Sensor to DETERMINE engine load so check the wiring to both sensors first for continuity and check for good connections. Chances are if it was a faulty TPS the transmission would default into 2nd gear instead of downshifting. If the wiring is good then check resistance at the engine speed sensor against a known good sensor or an established value.