1991 GMC Jimmy poor fuel economy, runs rough and check engine light fis on

1991 GMC Jimmy mileage: 147,000. I’ve been having problems with my vehicle lately. First, I had a check engine soon light come on. So, I had it put on a computer and found that the oxygen sensor needed to be replaced. A few months after that the check engine soon light again came on and it also started to use an excessive amount of gasoline. It also would run very rough at times and sometimes the whole vehicle would seem to shiver and shake. No codes came up so we istalled new plugs and plug wires. The check engine light continued to come and go off intermittently. We thought maybe the catalytic converter might be plugged so we replaced and it still used gas excessively. Last night our son was borrowing the jimmy and he said it started running very rough and then stalled and would not start back up. Today we cleaned the egr valve and the pcv valve and still the vehicle will not start. Any suggestions would be greatly appreciated. We have run out of ideas. Thank you.