Only towing issue with the M5OD should be the fact that, as the lighter duty transmission, they generally had 'high' gears - not the 3.73 and 4.10's that really rock for towing. You may find it difficult to maintain OD on the open highway, but 4th gear in my M5OD I'm right at 2000-2100 rpms which is where the engine's torque is the fattest - you shouldn't have much trouble except on the steepest hills.

Are you going to be towing *alot*?

My experience with the M5OD...I generally go back up to my grandpa's every 750-1000 miles to have the transmission refilled with lube. I run gear oil, as well. Gear oil is harder (relative) for the transmission to leak out, helps to keep it in there. Plus..its an older transmission so I like knowing its got that thickness for the synchro's. However, ATF is just fine if you go and get new plugs - GET the metal replacements ^_^. My grandpa never had trouble with the transmission, and neither have I. This is 220,000+ miles later ^_^