> Is earth gravity different in Death Valley vs top of Everest ?

Technically yes - gravitational force does decrease the further you get from the Earth.

However, the distance in question reduces the force by such a minuscule amount that it doesn't matter outside of science or engineering. You have to get very far away to notice - even the ISS, about 250 miles above the surface of the Earth, still experiences about 90% of Earth's gravitational pull.

From the calculations I was able to find, the difference in weight from sea level to the summit of Everest is about 0.4% - and that is about as extreme as you can get and still technically be "on Earth". For most practical purposes, you can treat the force as constant.

Edit: Just to expand on this, the highest city in the world is El Alto, Bolivia, at about 13k feet - half the height of Everest. A 50k lb shipping container would only weigh about 100lbs less if taken from sea level to El Alto - and that isn't a meaningful difference.