Mike -- Do not fear bias plys on 3-piece wheels. That's what I run on my 1-ton and I routinely run at highway speeds (`65 MPH) without issue. When I got my new tires mounted, though, I got them balanced. Above 65, which my truck is capable of, things begin to get a little ... uncomfortable. They are, after all, bias ply tires and do have their drawbacks. But 60-65 suits me well enough, so life is good. I am thinking that in a few years when it comes time to replace them, I may go with tubed radials.
But proper inflation is important for safety -- keeping those pieces together when spinning around fast enough to go highway speeds. The other important things are having good tires on good wheels. Keep those wheel parts clean and rust free. Properly inflated, good condition bias plies on well-maintained 3-piece wheels will give good, safe service at highway speeds.
Now ... How are your brakes? Your steering? Those need to be maintained, adjusted and and in spec, too.
Lastly ... got seat belts? Fire extinguisher?
