when ever i drive my s-10 faster than 55mph my check engine light will flash for a little bit then sit solid. if i stay under 50 for a couple days, the light goes off eventually. i notice when i'm driving on the highway and the light comes on, my gas mileage is rediculously low and i can almost watch the gas gauge needle drop. i've driven less than 15 miles in this situation and used over a quater of a tank.

 

Try getting it to come back on and drive it to Advanced or Auto Zone and have them pull the error code.

 

ran it through a scanner. says generic cylinder 5 missfire.