Leaderboard

@mcase, @Slartibartfast's spot on. You can even just pull the motor down pretty easily (it's 3 bolts I think?) and inspect the fan cage, give it a spin, check for debris or blockage, etc.

If one bar of the motor's commutator is worn through, or one of the armature windings is bad, the motor will have a dead spot, and if it stops on the dead spot, it won't start again until something else moves it. I would guess that driving at highway speed forced enough air through the fan to move the motor past its dead spot. This would not explain it blowing for a couple seconds and then stopping, though--that could be a control issue. Still, I would check the cheapest/easiest thing first. If the voltage test doesn't point to the motor, you'll find troubleshooting info, parts locations, and wiring diagrams in the HA section of the service manual. It's got separate diagrams for manual, auto without navigation, and auto with navigation, so make sure you're looking at the right one. Also, looks like the auto systems use a transistor instead of a resistor pack, so, that's different. Allows it to change speed gradually, I guess. Probably less likely to start a fire if the duct gets packed with leaves.

16" was stock for several years. I think even the pre-facelift trucks still had the 15" steelies and alloys that eventually made it onto the early Frontiers. Facelift LEs had the 17" wheels; SEs were 16". Doubt you'll have any issues.