I think 50K ?
Depends on how you drive it, I just had my 100,000 mile service done, they changed every fluid in the truck!!
I got the truck with 60K on it. And I tow alot between the camper and boat, so I change motor oil every 3K and the tranny every 2 years and all the rest every 50K, with ck's in between for leaks and stuff.
I once had a seal leak in the transfer case and did not know it, then in a winter storm I put in 4 wheel drive and blew the transfer case and tranny, cost me $2000!!
I always change my own oil, when down there I grease the front everything and look for signs of leaks, or torn CV boots ect..ect..ect..
If you are thinking about it then do it!! Must be getting close to that time.