OK, as a former shop head technician and service manager who has endured corporate product sales training of several large brand tire manufacturers, let me chime in on the subject for the OP. I have a '97 Ford F-250 loaded with an engine driven welder and other large paperweights… recently outfitted with D load range 285/75R16 rubber.
I think Tirerack has a great writeup and explanation of load ratings and inflation pressures. Check it out… you can learn a lot from their writeups.
First thing to think of is the load capacity of the tire, as opposed to its inflation pressure. A tour de France cyclist has over 100 PSI in his rail-thin bike tires, whilst my buddy who has a street-legal monster truck resting upon HUGE 5-foot high tires has only 6 PSI in his tires. 150 lb cyclist vs 6000 lb diesel truck.
Can you put passenger tires on your what I assume to be a 2500 Silverado (I don’t recall 1500 Silverados coming with the Steeltex). If you go with a P tire, your max inflation pressure will drop from the 80 PSI that Chevy chose to use 50 of, to 44 PSI on a Passenger tire (I don’t know of any P tires that have higher max pressures). Can you get down the road safely doing this? Probably, but don’t plan on carrying anything heavier than a paperclip in the bed, half a tank of fuel, and no passengers.
The Steeltex was an AWESOME product. Some bean-counters at Bridgestone are probably to blame as to why Firestone discontinued this product. I serviced a lot of vans and trucks with the newer Transforce AT product… and I have to say they wear quite well. Currently I’m running Cooper Discoverer ATRs that are wearing QUITE well after 12K miles. Now, you might be wondering why I dropped from an E load range tire which came on the truck originally to a D load range tire. My truck is a turd without 4x4 engaged, and isn’t that great with it. I hated getting stuck on flat muddy ground because the sheer heft of the vehicle (almost 7000 lbs empty), so I decided to go with something wider and a bit taller both for off-road handling and looks. The 285/75R16 D load range Coopers have nearly three hundred pounds MORE load carrying capability at its max pressure of 65 PSI than the E load range 235/85R16 tires did at 80 PSI.
Also, a lot of trucks list a higher pressure on the placard for the rear tires. This is because they assume the rear is loaded. A good trick to do is to inflate all-around to whatever you like, but then draw a few lines of chalk across your tread. Go drive around for a few miles, and see if the chalk is wearing evenly. If the chalk disappears on the outside, you’re underinflated for that SPECIFIC load configuration (you, the angry girlfriend, the dog, and a full tank of fuel etc), or overinflated if the chalk is rubbing off in the middle of the mark. Adjust accordingly for your everyday configuration to find that sweet spot (both front and rear pressures) that allows the load to be distributed evenly across the entire tread footprint.