Throws Belt

HELP!!!! DLI/B&M 177 on Mopar 383/484hyd. cam.850 Holley

Drove car for first time Thursday and stomped on it a few brief times and except for some tuning issues went OK.
Fri. night installed boost and fuel gauges so I could get serious.
Now as soon as you nail the throttle it throws the belt!!!!:angry:
Put it back on,crack the throttle,off it goes:shocked:
The idler/tensioner pulley gets warm but the bearing is free and smooth.

The belt is probably the original to the kit from Dick Landy Industries late 90`s at best even tho it had been used vey little.

Alignment is very good on everything,but there is some run-out on the crank pulley.

Also what is the trick to getting the belt on and off?
I have to wind it on and off by barring the engine since the tensioner is bottomed out before the ribs clear a groove?

One more thing: I got about 5lbs of boost just by nailing it in neutral ,
Is that supposed to happen?
Is that my belt problem too?

Fixed. Belt was set too tight. Getting new belt anyway.

Blower still LOUD. Sounds like 4cyl open exhaust engine braking at high RPM.
Only when its floored tho.:eek: