Are they a true "D"? I may be wrong, but I don't know of any of the single-axle D red KW's that could haul 13,000#. I wonder the same thing about their new single-axle Cascadias.
They are coming on as D trucks into the FedEx fleet. We can haul over 13,000# in our old Red KW DR truck with the tag axle down, and close to 5000# with it up. Take away the weight of the reefer unit, tag axle, lift gate and the extra weight in the box due to insulation and heavier construction, plus the extra load handling equipment a WG truck carries, and I would guess yes they could haul 13,000# or very close to it.
In our 10 months out here, we have only been offered 2 loads that came out at 13,000 and 7 that were 12,000 - 13,000# range. (Turned down 1 of the 13,000# loads due to low rate, and accepted the other but it cancelled.) We turned down 3 of the 12,000# loads due to rates, and accepted the others. Actually hauled 2 of these (both were surface loads headed to Laredo), as we did not get the other 2.
By far, most (70-80%) of our loads would easily fit in a "C" truck. We do get load offers that require a D due to the number of pallets (8-10), but weigh less than 5,000#.