newbie tekno-rc revo owner...

hello...i just finished my tekno-rc revo conversion (mamba max + Feigao 540XL - 9XL Brushless Motor (9trn, 5mm shaft, 74A, 1853kv) i only use 7.4 lipo battery on it. is that the reason why it runs very weak? or maybe the electi-clutch was the problem, totally confused...i will try to use direct drive to see if it will run better. still waiting for the parts from impakt RC. here's what i have ordered...
1 x Novak Pinion Gear (Mod 1, hardened steel, 5mm, 15t) (NOV5104)
1 x RC-Monster Electric Motor Mount (CNC aluminum, Traxxas Revo) (RCM-MM-REVO)
1 x *Tekno RC Long Shank Pinion (hardened steel, Mod 1, 5mm bore, 15t) (TKR4155)
can anyone tell me if this will help...thanks a lot