help with 2001 sportage

A couple days ago I was drving along and the check engine light came on. a few minutes later the car began to sputter and backfire. Then it began to lose power going up my street which is up hill. It was really having a hard time getting any speed . I took the scan tool and it came back with code p303 which is a cylinder 3 misfire. changed all of the spark plugs the light goes off start back toward my house same thing. Then checked for a vaccuum leak that was fine, cleaned air filter,replaced fuel filter, still having same problem any suggestions?

The description you gave is exactly my condition last spring, mine was P302. check THIS (www.automotiveforums.com/vbulletin/showthread.php?t=571775) out .
Did you pay special attention to the condition of the coil pack and spark plug wires? DId you see any trace of oil on spark plugs when you removed them? There is no doubt you have a spark problem and coil pack/wire failure and oil intrusion from valve cover gasket are common issues. Check inside of booth that covers the plug for spark trace.