Filling up

take it to the dealer, the early mustangs have a bad vapor valve in the tank that prevents it from filling up easy. ford issued a new tank for mustangs. many people here have had this TSB done. afixer posted many of the TSBs for everybody. the dealer will put in a new gas tank for you under warranty.
here the link to my experience with the gas tank......
http://forums.stangnet.com/showthread.php?t=549092&highlight=service+manual
and heres a link for the TSB:
http://forums.stangnet.com/attachment.php?attachmentid=34911

yea what he said. also make sure you have then order the tank protector some dealers have had problems removing the old one frome the old tank. also make sure you run the tank down as low as you can. and tell them that you have read all of the forum regarding this issue and if they want a good customer they better do their homework befor doing it. it is really a simple job i helped do mine. a couple of things make sure they are carfull when replacing the sending units and reconnecting the transfer line between the saddle tanks. good luck i have had no issues with my car since i have had it done.