1993 Chevy Corsica general questions

Several years ago my Corsica heat gauge would show it was hot after driving it a block or so. I took it to a chevy dealer & after much time I overheard that the problem was an engineering defect. It was "fixed" by doing a bypass job & I was charged for it. Every since, only sometimes, the car will begin to shake or kind of jump when driving down the street. I am very careful where I buy my gas, only Sams, Quik Trip or Kwik Shop. Sometimes it will do it several times in succession & then may be awhile. I am always afraid it might stall on me when I am on the road alone. Any ideas? I also have a dumb question - I am not a mechanic so I don't know where & how to get to the fuel filter to change it. Please help. I also have trouble with the Check Engine light coming on periodally since the heat guage issue. I check the fluids & that is not usually the problem.