I had a simial problem with my LRP Q2. I never had it with the original Quantum. With the Q2, durning a race only (never happened during practice) I would be several laps shy of everyone else.
I did two things at one so i don't know which was the solution but it never happened again:
1) I installed the large capacter from the LRP World's Kit
2) I move the location of the transponder. I had it mounted to the top of the servo. I moved it to the front bumber so the only thing between the transponder and the loop was foam and plastic...no electrical stuff inbetween.
These 2 things cured my problem and it never happened again on my TC3.
I have sinced switched to the 415 and I am running the same ESC and transponder. This time I have it mounted on the servo again and so far no problems. Because of this I have reason to believe that the cap. helped more than the change in location.
Try the capaciter and make sure that the correct transponder # is entered into the timing program.