Ford Fiesta 2001 56500 miles slowing on hills and unusual behaviour?

first of all,when was the car last serviced?? sounds like bad spark plugs and lack of fuel or poor compression...If oil is ok and the engine has been treated with some sort of respect...a car on 56000 miles should Not have any major problems..with the engine...like i say get the car serviced and should be ok....got nothing to to with wheels unless you are missing one or two....