There are many options in this size tire, a couple with claimed "LT" designation as well. LT just doesn't mean what people think it means, when its still a tire designed for trailers.
A LT tire is still a LT tire regardless of its intended usage. If your referring to the G614 RST Goodyear says it is designed as a LT tire that is intended for the Regional Service Trailer industry (RST).
The OP has a 40' tandem axle trailer that needs HD quality 16" or 17.5" tires with loads capacity in the upper 3k or even a 4k tire.
Just because your tiny 14" Carlisle works for your small trailer doesn't mean much. Apples vs oranges.
Tire recommendations/requirements change when we move into the big trailer domain.