Depends which one you want to replace. The SC tensioner is easy, a bolt and it'* done. The other one is messy because coolant goes threw it. You need to take the alternator off, the heater hoses, and will need new coolant elbows. But all in all, not real hard.

On a 2000 park Ave....remove battery and you have enough room to replace both belts... mine is supercharged. No motor mount removal is needed.

Whenever I need parts, I always try looking at Ebay first. I'm glad that I always found a good deal there. Dayco is known to produce quality parts such as idle Puller, tensioner pully, serpentine belt and the likes. But many also said that Godyear gatorback belts are much better than Dayco. I am yet to try that one.

My SC tensioner self destructed at 110K. Took the belt out with it. Parts came from NAPA, Gates belt and I think Dayton tensioner. Hardest part was loosening the motor mount enough to get the belts in/out.

It would seem on the Park Ave my Gatorback is working very well..no slipping & quiet.
Since the tensioner seems to be ok and it has coolant going though it, I decided to be on the safe side and get a new GM idler pulley ordered. With new bearings on the GM pulley, hopefully nothing self destructs any time soon!

Have to say the GM idler parts are steel and real quality bearings unlike some other vehicles plastic crap.The Old one was still in very good shape. Bearing still tight at 91K miles, so it did not need replacing but I put a new GM one in anyways.
It is a Left handed thread and was an easy install with a long handle ratchet, however the belt gave me a hard time as it came off the lower cam pulley.
Had to get someone to get under and get it back into the groove and then let ratchet free to tighten it back into proper alignment.
I called it a few foul names....
Used red locker on bolt. It aint going now where.

Nice job art!
Going to replace mine eventually, it is on the list of stuff to do, down that list, but on it!