Man of Maine: I run 700X15 six ply nylon on my truck. I will likely go to radials when these wear out, and it's been 10 years this year that they have been on there.

I use and drive my truck as it was originally intended; 35-40 on back roads so after the thumping stops and the nylong tires "warm up" they are fine. The only scary time I ever had was on scarified pavement and it was pretty interesting as the truck was squirreling all over the road with the slightest wheel movement.

There's a number of sources for radials and I will get the biggest diameter radial I can as long as it will fit the rim properly. I think the corresponding radial size is something like 215 75R or maybe even 225 75R. I think Bridgeport makes a 225 80R 15 but I haven't found a source for it yet. That might be a good replacement size for the 3/4 ton owner but again you need to carefully check the tire dimensions to make sure you can clear everything and look right on the original rims.

http://www.oldgmctrucks.com