I have a 01 kia sephia that lost power going uphill but on level ground it handles perfectly.

SOURCE: kia sephia 1998

I don;t know if you fixed it or not but the blocked on the spark pluges that is what is wrong yuo need to change them both out

SOURCE: Loss of power uphills and shifting improperly.

It sounds very much like your clutch is slipping. If the engine revs continue to rise when in gear and the car does not increase it's speed accordingly then if it is a manual car then you need a new clutch.

SOURCE: don't know how to check transmission fluid level for 98 sephia

while the car is running pull the tranny dipstick out and see what it says. the tranny dip stick is red. (well in most cars it is. some are labeld.)

rate me!! i wanna be a guru!

SOURCE: Loss of power/Engine Sputters going up hill

change your fuel filter it may have imputities in the fuel causing the fuel flow problems

SOURCE: No Dip Stick for trans fluid on 98 Kia Sephia!

Hi,
A little more info is needed... I'm assuming your car is an automatic transmission.
So the dip stick is missing? Or can you not find the location of the dipstick? The owner's manual will help you to locate it. If it is missing from the tube, I would recommend calling an auto salvage yard to get another one.
If your auto is a standard transmission, you can have the oil checked by a mechanic if you suspect it is low... rare, unless it's leaking.
Hope this helps...