Hallo Stephen, If you could let us know what upgrades you have we will be better able to offer help,
Is it new gearboxes ?
Perhaps Gearbox output shaft Axle bearings, or maybe a new control board,
If it is Photo-Etch then you are entering a different world of Tank building,
Whatever the upgrades we can help but we need a clue as to what it is your doing.
Shaun.