Built 700r4 problems..I need opinions....

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Ok I have a 406 sbc with around 500 hp +/-
Connected to a "built" 700r4
I actually got the engine and tranny together as a package deal.they were in a international scout that had a posi and 373 gears.

The fluid smells looks great and the overdrive cable is adjusted correctly...
I've been driving my car for around 2 months on this combo with no problems
shifted really strong in all gears!
now shortly after installing a quickspool with 456 gears the 2-3 shift seems to be "binding" under full throttle or not "shifting" correctly

when it does shift it doesent slip I think it could be a brake band for 2nd gear maybe.? how much for repair??

What are your opinions and what should I do having limited funds