I'm no expert, but it sounds like it is pulling more amps than the lipo can supply and that is the cause. Try it again with a different pack, a NiMh, or a higher output Lipo (C rating).
I noticed this on a very high bite track with my 3200 & 6.5 GTB set up in a 4wd. With my NiMh packs, no issues, but with the lipo, I got the hesitation unless I rolled on the throttle slowly.
--Joey --Venom Batteries & Chargers!!
Old School Racer & Vintage RC Car nut
RC10CE (X4),B2,B3,B4,B5, B5m, B6D - 10T,T2,T3,T4,T5M - B44.3
BRZ-444, RC10M, RC10L3 oval, L4 oval X 2