Old Whirlpool Gas Dryer Intermittent heat

I have a pretty old whirlpool gas dryer, serial no. FOO801282 that heats up when first started then the flame will go out. periodically thru the drying it cycle it will relight then go out again. It takes three or sometimes four cycles to dry a load of clothes. The flame sensor was replaced about two years ago. Thanks in advance. Seems to be a great forum here.

Still have not been able to sort out my problem. any advice?