Welcome to AF!
What gas station did you fill up at? If it was a Citgo, follow this procedure:
Though Citgo does have an insurance policy that covers any damage caused to cars by the gas they sold you...if you can prove it was their fault
Does it have the problem when it is cold? If not, it might be a sensor, possibly o2. This sensor does not 'kick in' till the car is warmed up, so it won't cause problems till it gets hot.
Did you check for any codes?
EGR would most likely throw a code, though it is not absolutely necessary that it will. To check the codes you would probably have to buy a service manual, since Autozoen won't check anything that old (i don't think). Or check the top of this forum, a manual for your car is stickied there.
Take the obvious diagnosis steps and check for spark, it's easy enough on that engine.
If none of the above, next step would be fuel pressure, though if it okay after 3k rpm, that probably isn't it.
My money is on the sensor. Check the manual to see how to test it. It is probably in there. If not, go to autozone, read the page you need out of a haynes (or actually buy the manual since it is the Bible for your car).