Are you sure you don't have some binding or resistence in your truck? Sorry if it has been said before, but if nothing else helps, its in the truck, i have learned this the hard way before.
Work because i gotta, play because i wanna
People here hate Nitro, I love it. I start it, run it about 50 ft from me and it dies, I go after it. Perfect exercise
Since he was running fine with his 9920, I doubt it, but it's possible I suppose. Even so, that low gearing should compensate for all but bad drivetrain drag!