Westlake trailer tires have a ST185/80R13D rated at 1709# at 65 psi. Westlake has won a couple of OEM contracts and have vastly improved their radial trailer tires. This size is about 1/2" taller than the tires you now have. Westlake has increased the speed restrictions on all of their radial trailer tires to 75 - 81 MPH.
Please remember. I don't do recommendations for brand names. This is just one of the few options available for much needed load capacity reserves and the extra speed needed for interstate hauling.