By looking at the specs these are the only differences I see between the 863 and the 863H.
863 Operating weight 7135 lbs. 18 GPM pump flow
863H 7180 lbs. 28 GPM
http://www.bobcat.com/historical_specs/skid_steer
With 5200 hours on it these are the things I'd check.
Change all filters unless last change hours are known.
Inspect and clean or replace case drain filters.
Drive belt and idler, check condition and tension.
Compression check on the engine to see how it's doing.
Chaincase oil to see if it's milky or overfull.
Quick attach pins for excessive wear.
Lift and block the machine, check all 4 axles for play(end and radial).