I can cruise all day at 65 MPH in my 1954 Suburban.

Lower RPM installing 3.90 to 3.55 Ring & Pinion conversion (you will need a 4.11 rear-end R&P ring carrier).
Buy/use an installation kit - your drive-line noise will noticeably decrease.

Radial truck tires on the original 16" wheels (gets a wider diameter that results in lower RPM.

No matter what you do:
- check and adjust all brake system parts
- check and adjust all front suspension parts
- check all front/rear sdpring attachment points