Just got back to AZ from picking up Hull# 1337 and drove it almost 2000 miles exploring TN a bit then across Arkansas (I-40 & I-30), Texas (I-30, I-20, I-10), New Mexico, then Arizona (I-10). Did 70 mph early on staying with trucks then pushed a bit faster thru west TX, but decided to slow down on last 2 days to 65-67 in NM and AZ. Gas mileage significantly improves at slower speeds and entire drive experience just much better around 65 for us and our 3/4 ton Hemi RAM. I think 65-67 will work best for us.