Volvo I-Shift Problem

I inherited a nightmare job and am looking for some advice. Customer replaced their I-Shift in their Volvo and now the truck won't move. Only trans faults I am seeing is P107694 for Gearbox brake. Dealer came out and calibrated but said it failed during calibration at the slip position check. Dealer tech also tried slip point test and said it failed. The clutch appears to be original with only 200k miles on it. I am a yellow iron mechanic that hasn't touched trucks in a long time (when did they quit being manuals?). The transmission is back on the ground now. Anything I can check before we send this to the dealer? I wasn't the original installer, and it seems there has been some parts swapping already. The last guy didn't push in the clutch cylinder during install, could that damage anything during installation? I tried the hold test on it and it seems to drift slowly.

Thanks for any assistance.