As

@Tom E-Tron pointed out, highway range will be significantly less than the EPA range. If the Hummer is expected to get 350 miles of EPA range, highway range at 75 mph will be well below 300, possibly closer to 200 considering the poor aerodynamics of the massive truck. And keep in mind you will never drive 100% to 0% on a long highway trip. The 350 mile EPA range estimate is from full charge to 0% charge. On a trip, you will stop to charge at around 10%, max out at around 80%. So your real range will be 70% of what you can get on a full charge, as long as you are charging 10% to 80% at charging stops. So 200 miles of highway range is probably realistic.

Welcome to the EV world, where highway range is always worse than city range. Not what the typical car buyer is used to.

That said, put a 200 kWh battery in a smaller, aerodynamic vehicle, and you could very possibly exceed 400 miles of highway range at 75 mph. When will a company produce such a car? The Lucid can exceed 400 miles on the highway with its 113 kWh battery, but it is a sedan and very aerodynamic. The Lucid has set the efficiency bar pretty high, higher than Tesla - assuming their production cars match what their prototypes were able to do. The Lucid also costs more than the Hummer - a lot more.