Tire load rating C vs D

I have been running Les Schwab APT 265/75 R16 Load rated "C" tires on my 97 K1500. Most of my driving is on pavement, but a fair amount on
gravel roads. No real off-road use.
I am getting about 32000 miles to a set of 4 tires (rotated and inflated per recommendations). I have been happy with the tire, except they seem to be prone to puncture when aproaching the end of their useful life. I assume that's just the nature of the beast, but I wonder if getting the next set at Load Rating "D" would make any noticible improvement? What should I expect in ride quality and tread wear? My local dealer says there would not be any significant difference, though he says I should use slightly less air pressure.
Any advice or recommendation appreciated...
. . . Kurt
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