I'm an old school guy myself. The new tensioner system is easier and better in a lot of ways. You release the tensioner by putting a socket on breaker bar and turning. I have a 3.3 so mine is different in some ways from your 3.0. First get a manual so that you can get all the info that is germane to your vehicle.
The squealing is either a bearing or the belt. Replacement is the fix.
3.0's have a problem with the belt coming off when splashed with water if the belt, tensioner and idler pulley are worn. I think it is actually a bearing problem. There are several fixes.
Replace the afore mentioned parts with factory originals.
Replace parts with the Goodyear fix which has grooved pulleys and a doubly grooved belt. Part number 49204K or NAPA has their own part number which I don't seem to have. This is belt and pulleys.
Replace with Dayco part #5060968 and replace the pulleys with NAPA ones, sorry I don't have the part numbers for the pulleys.

The Goodyear is said to be the ultimate fix for the 3.0 but is more expensive than the Dayco option.
There may be more but these are all I have. Good luck with your project!

 

Granz,

Go with the Goodyear fix. You won't be disappointed. It is not hard to install and is in my opinion the only one to use, hands down.

 

Thanks guys... It is much easier then the old school alternator adjustment. In fact it was so easy it is kind of embarrassing on how easy. Besides needing another arm on my forehead to hold the tensioner pully down while trying to get the belt on. It was very easy. Thanks again!