What gas and who's gas are you using?
What symptoms are you experiencing?
Gas from the big companies even ARCO has cleaning additives put in. It is possible that even with a quality gas and depending on miles, you may have an injector problem. Try lowering the concentration of cleaner if you are getting a CEL in the Sequoia. If it isn't back to "normal" after 2-3 tanks fulls, there is probably some other issue like a malfunctioning injector to take care of.