Do a good power shift and see if it grabs or just slips into it.

power shift? you mean shift without the clutch right

NO just slam 3rd to 4th one time and get right back into it.The better option (or how we get an idea of a situation in the shop) is to start low in 4th and slowly let it bring its self up, If it going to slip, Normally we can recreate the problem without being rough on a customers truck!
Most likely it is a clutch problem , but could be a pump problem as well. You've got enough fuel for I'd say 350-400

My stock clutch on my 97 with #11 At FF would slip going up a hill while lugging it. But that was a 215Hp pump. Sounds like the clutch I say through a south bend in it.

thats

Hmm that might be a bit high. i dynoed at 377/931 with 370's NO plate, gutted AFC, 4kGSK, starwheel full forward.


Adam

well i definatly is the clutch since im estimated at about 550hp to about 1000 ftlbs that im putting on the stock clutch, i dont think it is the pump since it started hauling a trailer with a chit load of torque

I dont think your pushing anywhere close to 550hp

I'd say with good tuning and a turbo you'll be at 400, right now id say your probably 330-370 depending on who tuned the pump!
As for the comment about the setup making more than 370 , I would suggest putting a plate back in and you will get better dyno results, Theres a very good possiblity your getting to much fuel too quickly!

i have a plate in it now i never took it out

Not sure where you got 550 from but its a safe bet your over what the stock clutch will handle. If your makeing 550 Im makeing 600.