Engine on 1990 Jeep Wrangler

Why is engine sputtering at high speeds? Oxygen censor has been replaced, tune-up has been done. Thank you if can help
me out.

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2 answers
You should have the fuel pump (pressure and volume) checked and the ignition system. Either of these could be your problem. Also have them check for a plugged exhaust system.
Check spark plugs and lines. I had a similar problem and this solved it on my 2000 Wrangler.