A few guys have reported some similar problems that you have been having in this thread:
http://www.rc-monster.com/forum/show...gm+low+voltage
If you read through it you can find settings that they used to try to correct the issues. Topas and lutach talk about the acceleration while braking issue on page 8. MGM has also released some firmware updates that you could try out. I think the latest out is 3.22