Bicycle Mechanics - Second wheelset - cassette problems...wrong cassette?

My current set up on my cannondale f600 mountain bike has a sram 7.0 cassette/11-34 and a shimano 9 speed chain. I purchased a new wheelset and tossed on a sram 7.0 gripshift powerglide II 11/34. The shifting seems to be delayed at times and under pressure on tough climbs it tends to skip, not really to another - sometimes it might, but it seems to skip in the same gear? It doesnt happen all the time, but it makes me wonder if I have the wrong cassette or an adjustment problems.

How old are the original cassette and chain? If they have worn together, then the shifting would appear fine until you change one piece of the puzzle, then the worn state of the chain would show up as poor shifting and skipping, since the chain links won't properly align with the sprocket teeth. It could be a simple alignment problem, requiring a slight adjustment of the chainline from one wheelset to another. Start with tose two possibilities.

Thanks for the tips, the bike has 600 plus miles, maybe 150 trail riding. So, not sure of that, could it be adjustments that need to be made when I make the switch?

Are the wheels dished the same way? It could also be that the derailleur is a little off with your new wheel. I switch rear wheels on the roadie bike a lot, or used to at least, and would have to make a small tweak to the rear derailleur every time. If the rear hub is moved one direction or the other just a tiny bit, you're cable tension on the derailleur could be off enough to make your shifting inconsistent. Something to check out, at least.

Impreza has a good point about the hubs. What kind of hub is in each wheel? If you have 2 different manufacturers of hubs your probably going to have problems. Can you list your: shifters, derailleur, chain, cassettes, and hubs. Sounds like you have Ford wheels, a GM tranny and a Chrysler engine.....