Hey Tiny Jaime,
If your suspension(steering AND brakes) are in good shape 70mph is no problem. I do it all the time on I-10. You just have to hold on tight. But remember, these trucks ( mine is a 59 tf)are not designed to handle like a modern vehicle, they were made to work slowly. Drive slowly, be careful and know that you can if you need to go a little faster, safely.
