The only concern with 6,000 lb. rated axles and the LT tires rated to 3,042 lbs. is that you may have a tire that is carrying more than 3,000 lbs. due to uneven load distribution, and that is mainly if you're right at your GVWR of the 5er. Before I bought the tires I have now I bought a scale so I could weigh each tire/wheel so I would know if any were carrying more weight.
"1. I feel a possible concern with the weight rating of the LT tires. I will be at the extreme upper limit with load capacity of these tires. As compared to the OE ST tires. Another question, are the LT tires overloaded when seperated from my truck, no weight on the pin?"
No, with the 5er off the truck the pin weight is now on the front stab jacks.
"2. Has anyone ever had a bad experience with an LT tire on a trailer?"
Yes, some have had issues, but many were the result of manufacturing defects and addressed by a factory recall. There is no guarantee that an LT won't fail, but the occurrences seem to be pretty uncommon. Personally I feel that there is no reasonable expectation that an ST tire "won't" fail. :)