maytag gas dryer will not heat

[cstet]

Maytag gas dryer starts to heat but only fires for 5-20 seconds then cuts of flame. This is e repetative action indefinately. I have replaced high temp thermostat, thermal fuse, coils and even the timer. I retroublshot the H-T thermastat by connecting the leads together and running the dryer…it ran indefinately. I also checked with an ohm meter which showed continuity. Does this mean the gas valve is the problem, or maybe the thermostat is bad; even though its new? This may seem like a repetative post but I have done all of what has been suggested already with no luck…Please help.