blocking egr fixes it but throws code...help

I have a 1990 with a 2.8l TBI I have done a major tune up and cleaned the throttle body inside and out. The truck has a slight hesistation from a stop and when I'm cruising down the road around 25-35 mph it jerks and stumbles. When I block the egr by plugging the vacuum line it goes away and she runs perfect. So I replaced the egr and tested the egr selenoid valve and it still does it. Its like its getting too much egr at lower rpms. It idles great with or without the egr plugged and if I stomp on it it has plenty of get up and no hesitation. just acts up when driving lightly. Anyone else have this same thing happen to them?
Thanks

I have a 1990 with a 2.8l TBI I have done a major tune up and cleaned the throttle body inside and out. The truck has a slight hesistation from a stop and when I'm cruising down the road around 25-35 mph it jerks and stumbles. When I block the egr by plugging the vacuum line it goes away and she runs perfect. So I replaced the egr and tested the egr selenoid valve and it still does it. Its like its getting too much egr at lower rpms. It idles great with or without the egr plugged and if I stomp on it it has plenty of get up and no hesitation. just acts up when driving lightly. Anyone else have this same thing happen to them?
Thanks

Mixture too rich ?