sometimes the connectors are the issue. try reprogramming it to the radio (or ur radio whichever) and starting from scratch. sadly there are cheap no-name cells in many 'hobby grade' stick packs out there. any idea on what gear ratio is in the truck? hopefully its a far cry from stock as it should be. i'm sure there's nothing physically wrong w/the trucks driveline but check to be sure. i'm pretty sure stampede comes with a gear diff so its not a ball diff slipping. idk if they come with a slipper, but ur not describing that kind of action/response.

try another battery? i still remove my motor connectors and solder the 2 sections of wire together on all my mamba systems (except the 1/18 stuff i used to do)...seems to help. but before u get into that. try the above and jump in the castle thread inside the manufacturer's tab (subfolder of onroad) and ask the men themselves if they can help. good luck

R