please help...bad cogging

[ncnguyen123]

i just got my gmaxx up and running on brushless and notice bad cogging mainly when i hit full throttle from stand still or go slowly. for some reason, it doesn't cog when i run on stand without wheels nor cog as bad when i hit full throttle in reverse. also, it doesn't cog as bad when i loosen the strobe but of course this nearly melts the pads. i even tried adjusting EPA but no luck.

here's my set-up:

BK 9920
Feigao 8xl
UBEC
14 cells, GP3300s
Strobe, 51t and 16t pinion

please advice...