2007 kia rio losing power when going up hills

Random misfires could be gas related- low fuel pressure, vacuum leaks or air leaks upsetting the air/fuel mixture ratio, clogged air filter or fuel filter. Could be ignition related- worn spark plugs, possibly. Or could be an internal mechanical problem-possible valve train malfunction.
Start with a fuel pressure test. check vacuum hoses for leaks, check intake manifold and throttle body assembly for leaks. If you have an exhaust leak at or near the engine, can cause misfires. Air going into the engine is metered by the mass air flow sensor in the big air boot on the throttle body. If extra air gets into the engine through a vacuum leak or a loose hose, the engine computer won't know it, so the air/fuel mixture will be too lean, resulting in misfiring. Several things to check-good luck.