Throughout a 20 lap run, you want to see consistent lap times when running "clean laps" i.e. not passing or being passed. The last JR3 race we ran at Capital City Spring Gobbler my son's ran 16 out of 20 laps between 12.026 & 12.193. That's a 0.167 min-max delta and honestly, I would expect to see that with tire fall off. Frankly, we still needed a tenth to run down the leader and have a shot to win. That's deadly consistent but it really took he and I two years to get to that point. I try not to beat myself by having problems like you described with your body dragging, but these things happen to me to. Keep learning and having fun with it. A year or two from now your driver will be good enough that you can give him a hunk of junk and he will still be able to wheel it!