'04 Tacoma 4cyl idles fine, but under load it shakes and check engline light flashes

i let my 2004 toyota tacoma 4 cylinder get really low on gas. i filled it up at a somewhat shady gas station. after refueling i drove home. the next morning on my way to work as i was climbing a hill my truck engine started shaking and shuttering and the check engine light started flashing. i put heet in the gas tank thinking i had watered down gas..it seemed to help but engine light is still flashing when motor is under load. i had 3 engine tests done at 3 different auto shops and no codes popped up. any suggestions?

 

When was the last time your did plugs?