I replaced my wheels with handbuilt mavic xm819's on XT hubs, much stonger than stock and at a halfway reasonable price, run tubeless with scwalbe fat alberts
As far as stems and bars I upgraded to a raceface diablous stem and Easton downhill bar in the 31.8 diameter much stiffer no creaks and I like the position much better for the tech trails I ride
Actually there is very little stock now about my slayer, the original parts are front triangle, brake levers, crank arms, shock and fork (both have been rebuilt though), and front derailler.
That being said I've got the bike performing like a champ, and am very happy with it the only thing I would consider now is possibly a repaint as that really shows it's age.