People really underestimate the amount of time that goes into shifting/driveability tuning at OEMs. Not exactly an action item that goes to an intern to knock out in a couple weeks.
Our local LKQ is light on Mercs at the moment, but they're pretty flush on BMWs. Know of any of those off hand that do better than others?
Check your PWM driver. The FETs do all the heavy lifting. So long as they aren't some generic black box garbage you're probably going to be OK.
That Merc fan is some good info. 50A...she'll do some work. I've been planning on leaving the mechanical fan in mine, but if one of these turns up locally I'll have to give this a try.
I'll keep an eye out to see how those 37s fit up with your axle placement. Mine lightly hit the front fender...