There aren't more plies in the LT version.
The number of plies thing is mostly meaningless nowadays. It goes back to the old bias ply tires when an E rated tire had 10 plies, a D had 8 plies, etc. Today everything's radials and it no longer applies, but folks still refer to an E rated tire as a 10 ply. All other things being equal, an E rated tire will still be heavier and tougher than a D rated one, which will be heavier and tougher than a C rated one etc.
My 3/4 ton dodge diesel came with E rated tires and I've kept the same rating tires on it. I rarely have flats or any other problems out of the heavy duty tires. I always seemed to have problems out of the standard tires I've run on other vehicles. In my experience the LT tires last longer and give much fewer problems than the standard tires. To me it's a no brainer to use them on a pickup.
