I was recently told by a mechanic that I should only use Shell, Chevron, or Texaco, because they are the only ones that have cleaning additives in their gas. I have two delivery vans with 350k+ original miles on the motors, each, and we have been using a lot of Shell the past few years, so that seemed to reinforce what he said.

There apparently IS a huge difference in gas quality. Especially avoid the lesser or no-name brands.