Just got back from a ~1000 mile trip to upstate NY pulling a trailer. Great trip. Very dry up north. FIrst long haul with this xterra and I noted that on those looong hills on I-81 in PA, the tranny (auto) would, as expected, downshift from OD to (I assume) 4th, when goosing it to keep from being eaten by the big trucks. The tach would jump from ~2200 to ~3000, as would be expected. However, on a couple of occasions, it seemed to downshift AGAIN (if goosed further) and the rpms would jump to ~4000. Presumably this last downshift went to 3rd. All the speeds were not less than 55-60 mph. Every time afterwards it would shift back up normally to OD once the load was off. A couple of times after the downshift-upshift sequence, I noticed that distinct odor of clutch (or perhaps brake pad).

My questions are: should it downshift that far (to 3rd) at the speeds noted? Was that smell a coincidence, like brakes or clutch from the big rigs or did it come from me (my truck, that is)? The X auto tranny doesn't have a pressure plate like like a conventional manual, does it?
The tranny fluid was fine before and after. No change in level or color or odor.
Your comments

Sounds normal, but I'd still keep my nose in the wind 'till I was sure about the smell.

When pulling a trailer, Nissan recommends turning OD off.

Automatic transmissions have torque convertors, which bolt to flex-plates and then to the crankshaft. There is not an air-cooled clutch in the bellhousing like on a manual transmission.

If you were only doing 55 or 60, the transmission probably shifted into 2nd gear. Most automatics are geared so that 2nd gear at redline can take you 70+ mph.