My garage overhead heater blows good warm air when I first start it up. After the first cycle though it only blows cold air. The flame rarely burns after the first time.

Probably time to call in a tech. Gas pressures will need to be checked as well as the gas valve, burners, heat exchanger, etc. Something is clearly wrong with the unit, and when it comes to a gas related issue, you really need a pro to diagnose the problem.