In Texas pulling a 5er that fast could land him a big ticket.
Texas Law states
"The maximum speed for a towing vehicle in Texas is 70 mph -- on the interstate -- unless posted otherwise. Under code 545.352, that's only in the daytime; it applies to passenger vehicles and light trucks pulling small trailers less than 26 feet long, carrying a boat, motorcycle or animals. For such small trailers, the nighttime maximum is 65 mph. For other kinds of trailers, such as fifth wheels, the maximum daytime speed is 60 mph, and that maximum drops by 5 mph at night. Common sense trumps the posted speed limit: If it's foggy, and you're still traveling at 55, the police can cite you for dangerous driving."