I dont agree with ABCellers, in my experience if the ignitor is bad the dryer wont heat AT ALL. And if it heats for the first or first and second attempt and then just doesnt catch the flame, its the heating coils every time. Thank you, Frank.
Without a doubt it is #3, the gas valve coils. Replace those and you will be up and rinning. You will need a phillips and a 5/16" screwdriver. If your phillips is so long where you must remove the drum, please note how the belt is hooked around the pulley and practice taking it off and putting it back on before removing the drum.