[Ray62406]

Hi, my 99 k3500 dually with a 6.5 diesel started shifting harshly a while back and then corrected itself. 1-2 shift could either be normal or snap your neck. It finally set a dtc of p0751 and now it doesn't shift to 2nd at all. I replaced the 1-2 shift solenoid on the transmission and that did not correct the problem. What I do know is that when in drive I can manually shift to second and it will go. Under power in 2nd it will slip which indicates low fluid pressure or bad clutches. There was not enough debris in the bottom of the pan to indicate any clutch damage. The pan was clean. I believe the 1-2 shift solenoid is not being activated and that is why it slips.
I traced the shift solenoid circuit from the transmission to the pcm and there isn't any damaged wiring. The solenoids are powered by fuse 20 in the fuse box and if it is pulled I don't have pndrl or tach operation so I know the fuse and circuit is good. I also know power from fuse 20 is feeding the solenoids as 3-4 and od is still working and they get their power from the same wire as the 1-2 solenoid.
Has anyone had any issues with the pcm failing and not allowing the 1-2 upshift? My thoughts were to splice into the wire between the pcm and the transmission and ground it while driving in 1st to see if it does shift to second. I know the pcm grounds the circuit so I shouldn't damage anything if I do.
If there are any tranny guys out there please respond.
BTW, the truck has 97k miles on it with very little issues. Thanks for any response...