My F150 with E4OD downshifts at the slightest provocation too, and it really makes me mad.
Back in the day I tried larger diameter tires but that was a fail. Stock size tires are the best. The piston speed calcs for it put it at too slow rpms at 55 so it may very well be that shorter axle gears would help. Mine's 4x4 so I won't be doing that.