Trying to plan for trans fluid change schedule for AT4 3500 HD carrying a 3000# camper practically full time.
While truck is 4wd much of driving around the country has been on paved roads in 2wd and/or Auto.
Not sure, but assuming this might qualify as "severe service?"
Additional Required Services
Severe Service Every 40 000 km (25,000 mi)
Change transfer case fluid, if equipped with 4WD...
Every 72 000 km (45,000 mi)
Change automatic transmission fluid and filter.