Geppetto - glad to hear that you figured it out. I was gonna mention to you that CVD slop can cause car hop on the track. Usually its the end that attaches to the axle. The pin hole becomes elongated and you get "backlash" in the joint which eventually shows up as metal shavings.
REEDY - If I was right in my assumption that you use a 78t spur gear, a 30t pinion would be a gear ratio of 5.72. Unless you have a HUGE flowing track, that ratio should fry just about any stock motor in existence and not be as fast on the track as a higher ratio. Even if you don't ruin the motor, that gearing is below the powerband of current stock motors. On most tracks, the GM3's powerband for gearing is going to fall between 6.6 and 7.2. Even in the mid 6 range, you risk broiling the magnets on a GM3 and leaving a nice trail of white smoke. The P2K's powerband lies lower in the RPM spectrum and can typically be geared from the low 6's (safely) on big tracks to about 7 where it will then lose against the GM's higher power band. At 27t, you're at 6.36 which is about as low of a ratio that I have ever run in stock succefully and that was in a low-rpm/high-torque motor. I wouldn't recommend any lower than that on most tracks. MVP is closer to GM3 than it is P2K as far as powerband. Higher R's and a higher RPM powerband. (This is my experience with them so far). Guys, anything to add?