If you fire it up and the burner goes on for a bit then off then back on, off etc. while leaving the thing running that is an indication of coils. Coils are simple to replace and you wont be messing with the gas system. Last time I bought coils they were $36.00 for both, repair guy will nick you 2 bills or so. You said you checked for lint, make sure you check from the filter housing, on,off,on, off is a symptom of overheating as well.
shamus