2013 Peterbilt 587 Sleeper Cab only 488k miles, live hydraulics wet line kit

2013 Peterbilt 587 CONVENTIONAL CAB, 12.9L L6 DIESEL. Runs and Drives.Has live hydraulics and a wet line kit. We’re told that it needs to re-gen but we aren’t able to force the regen with the switch on the dash. Right now the trucks moves very slowly from what we are told is this issue. There is an attached video of the truck running.