96 with 4.3 10

Transmission(4l60e m30, no removable plate at bellhousing)
started to act up 2 weeks ago. Had to go high rpm for reverse to work. But once it caught was no problem. Also felt like it stayed in 1st gear. Yet again had to go to high rpm and let off gas to up shift. Replaced with a 4l60e m30 no removable plate from a 98 Sonoma. Tried old torque converter and one that came with 98 sonoma trans. Same problem in both instances as original trans. What can be issue?

 

Replaced ecu last year do to corrosion and starring issues. Brand new and programmed. Also shows no cel and only stored codes were a knock sensor and one for a exhaust leak.

 

What are you using for a code reader? Maybe you need a big shop one to find out the issue. A bad crank pos sensor or cam pos sensor can cause shift issues.

 

Used a handheld of a friends and at autozone.

 

Not sure then. I'm lucky to have a local tranny shop that ran my code for free to find out my issue being a bad camshaft position sensor. It was causing my lockup on the TCC to click on and off.....