Well I finally got about 5 hours seat time in my M2 with Mercedes MBE 926 motor (300hp & 860ft/pds)& Allison Automatic.
The M2 is very different than my FLD120 which had a M11 (350hp & 1250ft/pds)& 10 speed manual trans. The FLD always had the same pulling power through each gear. The M2 starts out real slow, almost like it is winding up a giant rubber band. When you hit 3rd gear that rubber band lets go and man it really moves out. In a side by side drag race from a standing start the FLD would pull out a lead at the start but the M2 would be blowing by it within a hundred yards.
On the highway I still would choose the FLD over the M2. Once in 10th gear I never had to downshift even on grades of 4%. So it was very smooth even when you hammered the throttle. The M2 takes much more throttle finesse to keep the trans from hunting between 5th & 6th. There is definitely a techniques to this even though it is a automatic and as I gain seat time I think this difference in the 2 trucks will close up.
On secondary roads the M2 is definitely the winner. Don't get me wrong shifting has its moments, but there where more times I really wasn't in the mood, so the automatic shines here.
The M2 is definitely quieter in the cab, but the FLD was much smoother on the road with the Broc's ad-a-air front air suspension.
I could go on and on, but the bottom line is that the M2 is awesome and perfect for my application.
If you are use to big horsepower, want a truck that gets up to speed in a hurry, pulling a big trailer, live in the mountains, plan to drive in the mountain often, want to race your buddies in their conversions, than you do not want to even look at a M2 as a chassis for your next conversion.
2012 Showhauler 28'6" Motorhome on a Columbia w/ 450 Mercedes.