I replaced mine at 70K on one truck. The other truck I bought with 200K on it and I changed them when I bought the truck.
Plan to do it when you have to change the oil anyway, since you have to drain the oil to take them off.
Used Cloyes on both I think both of them have at least 30K on the tensioners now w/o issue.
The 2003 is a stock engine, and it took about an hour. Had to pop the upper intake loose to get to the one on the front. Much easier then the suggestion of removing the thermostat housing. No messing with fluids.
The 2011 has a supercharger and it took about half hour to change them since I could get at the front one with out removing anything.