Going 50mph on a moped isn't that easy on the bike. I'd recomend a motorcycle if you actually want to keep up for that 2 or 3 miles. Is there a large shoulder on the road?
I take mine out on the hiway sometimes, and just hug the side, and even pull off the road and stop if I have to, to let people by. Mine only does about 35mph.
You should check into your laws. Many can squeek by some of the laws, but 70cc might not classify as a moped in Texas.