04 3500 4l80e problem

[regcab02HD]

I've got a 04 3500 with a 6.0 and 4l80e. The other day I parked the pickup and everything was fine. I tried to move it 30 minutes later and the transmission wouldn't do anything. I had no forward or reverse gears. So I winched it on a trailer(while in neutral) and brought it to the shop to try and figure out what was wrong.

While it was on the trailer one morning I decided to see if it would go into gear so I could unload it. To my suprise it would move. So I unloaded it off the trailer and drove it around a little to see how it would shift. Everything seemed normal. It shifted normal with no hard shifts between gears. The only problem I had was when I tried to manually shift. I put it in 1st and took off. When I got to roughly 3000rpm the trans. shifted to 2nd even though the shifter was in 1st. I stayed on the gas and as I got close to 3000rpm the trans. shifted to 3rd. I drove it back to the shop and cut it off. Cranked it back up a few minutes later and it wouldn't shift into gear.

I bought a code reader and it gave the code p1810. (Transmission manifold pressure switch) So I bought one and replaced it along with the internal wiring harness. Got everything back together but the pickup still won't move.

 

The indicator moves on the dash and the rpms fluctuate momentarily maybe 50 rpms when you go from park to reverse or drive.

 

I'm still getting p1810 even after changing the manifold pressure switch.

 

 

Does anybody have any ideas of what to check next?