I have a 199? 7 speed Giant ATX 870 MTB that I use as my rainy day commuting bike. It has no-telling how many miles on it so I put a new SPRAM chain on and now it skipps when on the big/front small/rear sprockets under load. It was fine until I put the new chain on. I have adjusted the RD which didn't help so now I'm guessing it could use a new cassette. My question is, does this bike have a freewheel or freehub? It does have shimano components.