Toyota T-100 Towing Capacity

We're just ending our Chevy 1500 V8 Silverado truck lease and turning in our Nash 22 H Model trailer because the Chevy has been replaced by a smaller SUV and I can't tow the Nash with my Toyota T-100 truck. I thought for sure I could tow any of the Trailmanor trailers with my 5,000 pound/500 tongue T-100 towing capabilities claimed by the manufacturer--but posts here and elsewhere sometimes tell me I can't. I attend geology field trips sometimes 3 times per month and the comfort of a trailer is really rewarding. The TM is just about the same weight as any of the undesirable soft sided pop-up tent trailers with a shower--so the decision to buy a TM is easy. Living in Southern California, there is always a pass like the Grapevine or Cajon to consider. I would greatly appreciate any experience from anyone towing with a 4x4 T-100 before I plop down the money on something I can't tow.  My 96 T-100 does have the V6 with the larger engine introduced in 95.

Thanks!

Joan