4L60E Stuck in 2nd Gear

Have not posted here in a while but I really need some advice, help, or confirmation of what I am thinking.

Customer of mine brought me a 2000 Silverado 2500 with a 5.3 and 4L60E with a badly toasted trans. Took it apart and found 3-4 clutch pack toast, all bushings badly worn, pump pocket worn badly, input shaft loose in input drum, and tons of metal in the pan. Lots of parts later and we had a fresh rebuilt transmission.

Now that the transmission is in it will sometimes shift just fine through all gears with no problems. Then at times it will just be stuck in 2nd gear. I can use HP Tuners to command 1st, 2nd, 3rd, and 4th and it shifts fine when maually controlled with the scanner. The ECM just commands 2nd gear and holds it there. I have tried another computer and it seems to work fine with it and shifts properly. The computer I tried is out of my 79 4x4 build and he is not getting it.

I am thinking it needs a computer but wanted to see what some of you thought about.

I do occasionally get a P1810 pending but it has not went current yet.

Okay, I had some more time to read through the P1810 diag tree. It states that if the pressure manifold looses its ground. Then the computer sees that the transmission is in 2nd gear. When this does not correspond with the Park/Neutral switch it can hault all electrical control.

So when I get off work later I am going to pull the pan and swap out the pressure manifold for another one I have. Also might add a supplemental ground to it for good measure encase there is a ground issue in the harness.