[RC-Monster Mike]

The motor and gearing sound fine to me(I run a nearly identical setup in my truggy) - only 38mph or so on 5s isn't asking for too much. I would look elswhere as the pimp suggested(solder joints, etc.). The fact that the fan on the mmm comes on after a very short period of time with no load indicates to me that something is amiss somewhere. Others are running for 15 minutes with the fan never coming on.