Bob: Not at all. On highway trips I typically drive my '52 GMC 3/4 ton around 63-65 MPH. I've had it to 75 (with a tailwind). It has the original 228 GMC engine. Updates include a 3.55:1 rear gear and disk brakes. Engine specs say max HP is at 3400 RPM. If I could get it spinning that fast it would go 83 MPH. I'm not THAT stupid.

I don't know your tire diameter, but if it were 29" at your current 50MPH top speed you would only be turning the 235 to just under 2400 RPM. 60 MPH would be 2858 RPM.

'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.