TRANNY TRANNY TRANNY you'll never get close to that 600 mark without beefing up that tranny
I made 588 with an almost identical setup (Mp8 instead of powerpuck) and agree with the 120's.i made 582 at TS this year with my 03 ddp90's floor it stage 3 and a 66/71/14 turbo smarty tnt/r and power puck. so you will breeze 600 with the twins but if i were you id go with a bigger injector in the 03 i would do atleast 120 with twins 180s would work great.
problems the 03 04 trucks have that the 04.5 up trucks dont is the injector bodies are prone to failure cracking, wearing causing them to not build rail pressure the way they should causing hard start issues and ruff idle. worse than the newer motors.
Air Dog, Mitusa, Fuel Boss, Fass they will all take care of you.Here is my tenative list:
Southbend/Valair 3600 DD
MP-8/ Dr. P
S300 over S400
2nd gen intake manifold/ CFM +
What do you think? Obviously I'm missing a lift pump. Suggestions please.