Ok I'm driving down the Interstate on my way home and I notice I feel like some jarring or shaking towards the rear of the 4runner. But I figure it's just where the mud tires have worn unevenly, and that I'm noticing it now because I hardly ever get on the Interstate (5 miles round trip to school no Interstate). But I get to my exit and the check engine light is on. Now I'm thinking maybe please don't let it be the differential or transmission slipping? What should I check for? I'm mechanicaly brain dead so seriously I have no idea. This is my only transportation so if something is bad wrong I'm SOL!!!