To make a dryer run a long time it needs to have the lint cleaned out inside which means you must dismantle it. That means the drum has to be removed. When you have dismantled it look at the belt and see if it is cracked or starting to fray along the edges. Replace it if necessary. Remove the rear support rollers and check the bearings. If they are sloppy or are seized replace them. Check the idler pulley and lube it. If you remove the drum support rollers note the condition of the support shafts (dont loose the washers on either end of the rollers). Also when the drum is out check the screws for the baffles to make sure they are tight.