Could be lots of things. Could be a bad tranny. Could be a dying altenator & battery. Could be a leaky fuel line or vaccum hose. Could be a problem in your electricl system (plug, wire, cap, rotor, etc.), and it could be worse. You should try to diagnose it more by seeing if anything else is acting funny. Are you getting any interference in your radio or dimming lights? Is your charge light coming on? Does it seem like its electrical, mechanical or fuel related? Do you smell gas? Do you go through too much gas? Do you hear a whistling noise?