First what emissions code is on your engine emissions control label. The label is in your engine compartment. The code is in the upper left hand corner of the label. It would start with a "R".This will tell me what engine you have and what emissions system your car is equipped with. Then I may be able to help you check your EGR.
Also, at the 50-60 mph, does your cruise control work properly after the service engine light comes on?