Belt question

I can only speak from personal experience. On both of the 5.0's I've owned I have never had to "fight" to get the belt on. Now I admit that getting the tensioner all the way over and slipping the belt on at the same time with out smacking yourself can be a treat, but not a real problem. Every belt I have replaced has had the tensioner pointer either a third of the way towards the "tight" side of the range to smack in the middle or somewhere in between. You never said where the pointer was with the first belt which is the next clue, your tensioner could be shot and not putting enough pressure on the belt if the pointer was somewhere around the middle of the range. Like the computer geeks say, we need more data!

good grief! well at least you figured it out

How was it routed?

These are acceptable ways to route your belt. They are routed different both all are ok.
View attachment 502275

A good rule of thumb is that the smooth side of the belt should be touching the smooth pulleys (non grooved) and the grooved side of the belt should be contacting the grooved pulleys. If you have the belt routed where the grooved side of the belt is touching the smooth side of your pulley then something is routed wrong.