I would think that Pulling a sled would interfere with recovery. My legs take a good4-5 days to feel "recovered" from a workout. Throwing in sled pulls would definately lead me to overtraining.
I usually use an eliptical machine. The arch in my feet is too low and causes me to get shin splints if I run, so that's out of the question.
I just joined a new gym with a stepmill which I look forward to trying out this summer.