If you were to just hit the gas without touching the steering wheel in an empty parking lot with the wheels locked to the left or right--would the X keep turning in the same circle? Have you tried this?

When I'm parking the X between two cars--I want the wheels to stay locked for some period of time. For me, the "effort" to unwind the steering wheel back straight has never even crossed my mind because it takes very little strength.

Now, I drove a Chevette in high school that did not have power steering and it took much more effort on any turn than my '01 or '02 Xterra.

On front wheel drive cars I've owned--there was definitely the unwinding of the steering wheel(without my hands on the wheel) as you refer to.

However, I currently own a rear-wheel drive car that if I repeat my suggested parking lot maneuver mentioned in the first paragraph above--it always unwinds itself and turns in a larger and larger circle until it takes little effort to straighten out.

In summary, I'm not of the opinion that your experience is normal for an Xterra. My suggestion is to keep dealing with different Nissan Techs until the problem is fixed or look into the Lemon Laws in your state.