Yes, we had this exact issue looking at Christmas lights a few years ago. One of our rear brakes wasn’t releasing completely. We were driving slow without a great deal of air movement, and I couldn’t tell the brakes were dragging. Our 05 e4 kept throwing the 41 error.
After checking the usual suspects of dragging brakes, loose wiring, corrosion on terminals, and the controller being secure to the plate, I would still recommend a heatsink if you are going to be doing lots of slow moving driving with a large load. Check out: Controller Heatsink Upgrade
@RS_E6 went with a beast of a heatsink, and I think it looks awesome on top of the function 
A heatsink can be purchased from 10.080" Wide Extruded Aluminum Heatsink - HeatsinkUSA