my gf have a 98 teg LS auto, and lately her car seem to be not running as good as it should...i done all maintenance including spark plugs, filter, oil change, make sure all fluids are filled, etc.....when she accelarate the pedal seem to be hard and when she goes above 60mph and want to go faster it takes a while to get up in speed....i was thinking of doing the valve adjustment to see if that fix the problem....anybody else have any other suggestion?