Wonder if transmission issues are related to the clutch release slave/master cylinder? Perhaps it simply needs to have air bled from the system. Certainly can make it hard/impossible to shift until you stomp it a few times since the clutch would fully disengage given enough air in the lines. I've had it happen to me before. Unless he installed the wrong transmission fluid. I suppose that could cause some drag/coupling until things warm up.
Good luck. I'd try a dealership. Sometimes the prices for service can be quite reasonable and they usually get it right or make it right.
2019 Coachmen Freedom Express 204RD
2011 F150 Super Crew FX4, 5.0L V8
Husky Centerline WD Hitch