The need for you to over tighten the belt may be you have the wrong width belt. Some replacement belts are not the same width as the original which can cause them to slip. Also I remember having one replacement brand belt stretch (can`t remember the brand name at this time) causing it to loosen.
I had a car one time that would not charge good when the eng revved up. The more rpm the eng did the less it charged. It seemed like it would be a slipping belt but it was not making any noise or squealing at all. But I noticed if I started the car and then brought the rpm's up to about 3000 rpm for about 30 seconds I could see it charging less. Then I shut the car off and felt the alt pulley and it was so hot it was almost red hot. Which was from the belt slipping of course. So I found that to be a good test when I feel the belt may be slipping and its not making and noise. Just look for a very hot alt pulley that will burn your finger so just touch the pulley real fast when doing that test ! Put a new belt on it and problem fixed. I have seen this a few times in the 40 years I was turning wrenches where the belt slips but does not make any noise. Course the key is that it charges less when the rpm's go up and it will fool you for a minute since the belt usually squeals when its slipping. Ron
