Idling stumbles like head gasket bad?

When idling the engine stumbles as if the head gasket is bad. King says there's bubbles on the dip stick. I have not seen them. When traveling the engine does not stumble or miss but seems like it should have more power. We are opting to replace head gasket. It gets up to 70mph decently. I would not want to try to pass someone going 65 however without a mile and half to do so. I have not had the car long enough to know what normal is. Replaced the thermostat and changed the oil. Someone said it needs a head gasket. What say you? Thank you- Kristine Delaney