Yeah, unbolt one end of the tensioner shock and you will probably find it is bad. I had same problem on 6 cylinder. New shock made a big difference. While you have the belt off, check all the pulleys for dirt or such stuck to one of the them. Check the alternator for free, smooth spinning too. I had an alternator sieze on a 603 motor and it broke the power steering pump loose from the engine from the sudden yank on the belt. (and that is a special pump)