[Al Skierkiewicz]

Guys,
You should invoke Nottke's First Law of Maintenance, "Go where the last person was." (Rich Nottke was a very knowledgeable guy I worked with a long time ago.) What this means is look to the last thing someone touched or changed as the source of the problem. Sanddrag, you said you changed the motor and transmission so I am suggesting that the assembly is misaligned or mounted in such a way as to increase friction and as such draw way more current.(enough to seriously load down the battery.) Check that all is correct and the hardware is tight but not too tight. I bet you find it.