1998 Kia Sportage Kia Sportage runs up hills 2mph *help* *o

1998 Kia Sportage Four Wheel Drive Automatic 99,764 miles

When I drive my Kia Sportage 1998 up the hill, it goes rly slow around 2mph, it trys to go faster but still goes slow, rpms are 500 instead 1000 when I try going up the hills. I was guessing it was a oil filter, fuel pump, or excelator, im not sure what it rly is, dont want to waste money that its not the problem, help please.