There is no possible way to tighten the belt that much without bending the belt tunnels, which misaligned the idler/tensioner. This belt tunnel deformation is why you are losing the belt.

My belt is adjusted with zero slack, it will only skip at WOT on the street with the brake EPA set at 100%. At the track I can't adjust in any more than 50% brake EPA without locking up ALL FOUR WHEELS, and testing on the street with 50% EPA at WOT does not slip the belt.

Since I never race in the street, it's never a problem, and even if I did, I have a chassis brace to keep the belt tunnels from deforming so it never will be a problem.

If you're having belt problems I feel bad for you son,
I got 99 problems, but the belt ain't one.