I'm pretty sure there is something wrong with mine. Mine is the radio shack version, but should be identical to the Nikko thor with the single 540 motor.
From what I remember (I worked at radio shack in the late 90's) This truck had good power and speed, it would pull a a wheelie and blow through grass with ease.
Mine, is very under powered. Struggles to go through grass, can hardly drive up a incline and can't come close to doing a wheelie.
I tried 3 different battery packs (they work fine on other R/C's)
I tried a different RS540 motor.
I tried a different transmitter (thinking maybe the pot wasn't seeing full forward).
I measured the voltage right at the motor at full throttle, and it measured full battery voltage, no loss at the ESC. (free wheeled, no load). I measured the voltage right at the Mosfet, and only saw like ~.07 loss. (free wheeled).
So the ESC doesn't really seem to be "bad" unless it's going weak under load, but that's a little more tricky to test for.
Maybe I've gotten use to driving R/C with mod motor's and am expecting a bit much, but how much power does your have?