Before you go adding on to your engine, adding un-needed parts. Try fixing the problem you have first. The Sportage is quit good at hills, just remember you can't do it in 5th, your going to have to gear down if you want to pass on a hill.

As for the lack of power, like mentioned elsewhere check the Cat, they are notourious for falling in on them selves, you could also check the spark plugs and coil packs, and timing belt. But the simplest check is the air filter and fuel filter.

Once you have solved your lack of power issue, then you can add on to your engine for even more.