The long-range version of the Semi can go about 500 miles on a charge, about half of what diesel trucks can do. Some critics have questioned whether Tesla can meet its price and performance commitments, given the unprecedented size of the Semi's 1 MWh battery.

The 300-mile-range vehicle will reportedly run $150,000 while the 500-mile vehicle will cost $180,000. Those prices are still more than regular semi-trucks, but most observers believe that Tesla needs new battery tech to meet those goals.

DHL's transportation president Jim Monkmeyer told the WSJ that the Tesla trucks will ferry automotive and consumer product freight between factories and distribution centers. The runs, while local, could be still be hundreds of miles long.

Most buyers, including Walmart, Canadian grocery chain Loblaws and trucking firm J.B. Hunt have purchased the Semi in relatively limited quantities, with the aim to evaluate the economics, safety, reliability and other factors before making larger purchases.

At this point, though, they're more excited about the potential of the Semi than concerned about Tesla hitting its promised 2019 delivery date. "I don't know if we can count on specific dates," said Monkmeyer. "We understand the challenges that they are facing. This is the future and we want to be in on the ground floor."