I have 185k miles on my rig and it has the stock belt tensioner on. I've never had to diagnose a bad one so it's hard for me to say if mine if bad. For the most part the tension that it gives seems to be pretty firm. Should I still swap it out on the fact that it almost has 200k miles on it?

 

As long as it has full movement/travel, and the belt doesn't squeal. Leave it alone. When and if you decide to replace it, get a Dayco unit.

 

+1 leave it alone until it starts ticking, squealing, jerking, whining, or belt jumps off or doesn't track straight. then +2 on the Dayco.