The 255/75R17 size is the OE Jeep Rubicon size, and because of the intended application, I don't think there are any made in load ranges higher than C. The 255/80R17 tires are intended for 3/4 and 1 ton trucks, so they are all LR E.
As an aside, LR D is pretty much dead. Because all new 3/4 and 1 ton trucks have TPMS that wants to see ~80psi in the rear tires, all mfg's are now certifying their heavier light truck tires to LR E, which is 80psi max. (LR D was 65PSI, and therefore won't work on a newer truck.) As older certified LR D tires get discontinued, the LR D rating will become extinct. Honestly, in terms of tire weight and flexibility, there's not enough difference between a D and an E to even be talking about it.