Let me explain a little further: I just traded in a Model S 85 D two weeks ago for a Model S P100D. With a 40 amp cable the 85D charged at 30 mph under the same conditions, my new P100D charges at 27-28 mph with the 40 amp cable.
Are you using the same connector? All 85's came with the 50amp rated, 40 amp supplying connector. (Gen 1) I believe that all Teslas are now shipping with the 50 amp rated, 32 amp supplying connector....8 amps less (Gen 2). Gen 1 adapters that have no length of cord attached to them. Gen 2 adapters have a short length of cord attached to them, just FYI a way to differentiate.