TKO shifting issues at high rpm's

[6D9]

I am considering going with a TKO 600 for my next tranny. But I remember quite a few posts on the Mustang boards about these trannys not liking to go into third at high rpm's. They said the sucker flat out wont have it! Also will these things handle clutch dumps with ET streets and a 500HP 408sbc??? Thanks Ron