Dryer stops after 15 minutes and will not restart

Hi,
I have a gas dryer model 97585210 that stops after about 15 minutes in a cycle. Once stopped it will not restart. here is what I have already done.
taken apart the drum, replaced the 2 rollers in the back.
Vacuumed below the drum area and in the back by the blower assembly.
reassembled the dryer, and attempted to run a load again... after 10 minutes it stops...
taken apart the dryer, and with out installing the drum the dryer runs no problem...
installed the drum, and ran the dryer empty on air dry... the dryer stopped after about 10 minutes...

Im looking for suggestions...
thanks

alex