I have a 1998 cheverolet malibu and when i press the gas sometimes the rpms constantly go up and down.?

Question

Do i have a passing gear in my car?

Answer 1

THERE IS MORE THAN ONE GEAR IN EVERY TRANNY THAT IS WHEN YOUR CAR SHIFTS

Answer 2

the term passing gear is just a lower gear. When you want to pass someone and you need some extra power you press down on the gas pedal and the trans shifts down into a lower gear, [hence passsing gear.] It also shifts out of "passing gear at around 70 mph"
Hope this helps you out. as far as the rpm constantly go up and down. that sounds like your cruise control is going bad.