The cap covering the adjustment is different on the last models of 722.3 and 5 trannies. The cap is designed to be squeezed to remove on the plastic ones and usually is partially broken by prying. I keep spares and just replace them if they won't hold. There is no way top squeeze it properly with the trans installed.
You will probably need more than a couple flats of adjustment. Making it shift a little earlier with the cable adjustment will also help.
Bosch Master, ASE Master, L1
33 years MB technician