How big is your wastegate? Have you driven it down the road yet, how long till you start getting boost in the interstage piping?
When your truck is idling, is there enough exhaust flow to spin the big turbo, or does it just barely move and stall every now and then?
For example, on my 95', my 60mm HE351 spins at probably 5000 rpm at idle and my HT4B 83mm spins at 200 rpm at idle.
My setup has a little bit of lag around 25 psi boost where the wastegate fully opens and the HT4B starts coming to life, but it has GREAT top end power.