I don't often weigh-in on these tire threads because they get out of hand real fast. But since I caught it on the first page, I'll go for it!
In the last 2 years, I've invested a substantial sum of money in tires for different work and equipment trailers (plus boat and RV). By a quick count, I have a total of 24 Gladiator ST's (from LR C to LR G). So far, they've held up extremely well. Due to the nature of their use, they don't get checked very often and since my employees get a mind of their own sometimes, they see all kinds of speeds.
You should be able to get LR "D" tires in that size for about $80 each. Your listed GVWR seems way too high for the factory to have installed LR C tires. For my money, I'd go with LR "E" tires, which should be in the $90 each range (if my memory serves me correctly).