I no longer have my 84 K5 Blazer. After driving around a '96 Nissan Maxima, I now have an 83 K10. It has dual saddle tanks, one on each side. I just got it a few days ago and when I fill it at the pump, the gas keeps backing up the filler tube and triggering the automatic cutoff on the pump. I have to hold the nozzle half out of the filler neck and fill it very slowly to keep it from triggering the shut off. It does this on both tanks. Also, when I'm accelerating, sometimes it will run rough for a second or two and then smooth out. It idles fine and cruises fine. Would this be an ignition or carb problem? Or could this somehow be related to the tanks not filling up easily, maybe some kind of vent issue? It has a 350 with 8,000 miles on it and a Holley carb. Thanks.