I'm working on a 2003 model year and I can't seem to figure out which pulley is the belt tensioner. I believe it's either the one under the alternator pulley or the one that has no grooves for the belt and is to the left of the alternator pulley. When I loosend the bolt on it the pulley came loose but it didn't release any tension on the belt. So is that the tensioner or what?

Releasing the tension is a two part event. One is to loosen the both on the tensioner pully which I believe you described. The pully is smooth and not hooked to anything like a pump for example. Then you there should be another bolt just below that if you are looking at it from under the van. Thant both is what actually moves the pully up and down adjusting the tension. I believe the bolt/nut is bronze colored. My van is not at the house or I would tell you exactly what color it is. Good luck