one thing i would suggest is to ride with others that know the paths. and find some more technical trails.

they will more than likely ride faster than you and this will keep you pedaling harder.

i found that when i started riding with others it suddenly got harder. i could go ride ten miles on the street or 4 or 5 in the woods and it seemed the same, by myself.

i went on a group ride and after two miles, i was beat.
these guys just kept going and going and going....

but this may not be the case w/ you if your a roadie and in shape. i'm not in the best of shape but i do have better bike handling skills than most.
that is the only thing that let me keep up w/ the guys in the group, more than likely.