91 Lumina Euro 3.1

I'm new to the Lumina world so you guys are a big help. I just got this car and was driving it on the highway this morning. This may be a stupid question, but I was turning 2500 RPM @ 70 mph. Is that normal or am I not getting into 4th gear. Is there a fourth gear? The shift selector doesn't show overdrive, just drive. (Stock tires and wheels sizes)

Does it have a circle around the D, if so you have the 4spd o/d trans