Diesel Bombers - '02 Cummins won't launch

See description of my truck in my bio.

I've been battling this for a few weeks now, and I've tried to find as much information online as possible before making this post. Although I don't normally agree with making a new account simply to ask a question, I can't seem to figure this one out.

I've had this truck for several months now. Bought it as it is in the bio. I can remember it at first being extremely quick, and boosted launches were no problem (that was a mistake) I undoubtably lost the transmission a month and a half into owning the truck. I replaced the tranny with a Jasper racing heavy duty transmission (I realize this is not comparable to say a sun coast stage 2, but that was a bit out of my price range). Since that was replaced, my truck on the bottom end does not respond the way it used to. It seems much slower and any attempt at a boosted launch ends in failure. I am completely aware of how to boost launch,so I'll leave those details out. I can boost to 5psi, and when I let off the truck lugs down, looses the boost, then picks up and gets on its way, but buy then anyone I was racing is long gone. I try to build up boost slowly, and if I build anything over 7psi, it sounds like the truck de fuels, or backs down, and I have to restart the process again, and like I said, the truck simply won't launch. I can only think this is related to the new transmission in the truck. I don't think the clutch is slipping (though I can honestly say I don't know the symptoms of slip that well). I've played with the Edge some, the backdown is not interfering at all, I'm not throwing any codes, and on the top end the truck goes like stink. So this is where I'm confused.

I will be glad to supply any missing information. The truck is basically a daily driver, so boosted launches are a rare occasion at best, but I can't help but think something could be wrong, and I'd like to figure it out, as it didn't seem to do this before..

Any help is appreciated

Thanks
Brian