I've heard the mtb trail up Monroe Truck Trail aint all that bad according to my mtb friend and member "Eyemage". I haven't done it myself but have done Sunset up to the Potato MTn overlook which is a muthuh of an mtb ride. Eyemage has done Sunset to Baldy Village, like an mtb version of the GMR ride to the village. This makes the Monroe Truck trail to the shack a "not so bad" ride IHO.

As far as tougher than the road ride, not sure. But one time we left the bottom of GMR the same time an mtb'er headed up Monroe. We got to the top at the same. He said,"wow you guys must have been moving to get up here at the same time as I". Not sure what that meant, either he thought the road was tougher or longer, not sure.