Ok I have a 2000 sd 7.3 auto with a few mods I am having a problem under hard acceleration from a stop

It feels as though 1st gear is slipping then slams into 2nd and barks the tires forgot to mention it has a 6.5" lift and 35" tires

I am thinking it is getting to be time for a tranny wanted to know what others thought of my situation and of the different aftermarket trannys out there

Right now I am looking at the Diesel Site Monster Box and the TS Pro-loc

Thanks for all your help