97 cavalier overheating

New to this forum so any advice/help would be greatly appriciated! I have a 97 cav that is overheating at speed, not idle. Have replaced thermostat, water pump and hoses. No air in the system. Still overheating at speed, not idle. Was told by a mechanic that with this engine,2.2, and milage, 133k, the culprit is most likely the head gasket. Sound plausible? I'm at a loss.

It's quite possible. Take the coolant cap off and rev the engine - if the coolant starts flying out, then you probably have a head problem. But that's just a backyard mechanic diagnosis. It'd be worth it to have someone check it out thoroughly.