According to Leno, this is a replica of a high-speed transport truck Mercedes used for its racing program back in the SL's glory days. The original would do 108 miles per hour, which is kind of amazing for a vehicle of this size and layout. And remember, it carried that speed with a racecar on its back, allowing the mechanics to take the car back to the factory for service quickly. The key to this frankly blistering speed was the original truck's engine – a 3.0-liter straight-six from the SL.
Leno's example is a little bit different. See, Mercedes crushed the original transport truck in 1967. After realizing the error in its ways, MB built an exacting replica of the truck at a cost of around $2 million, and you can see that car in the company's Stuttgart museum. Leno's particular truck isn't a Mercedes-authorized copy, but was the creation of a Swede named Sergei. Leno took Sergei's body work and made it roadworthy, so he can use it as a transport. Which, you know, was why Mercedes built its version in the first place.
Those changes included adding a hood to access the A/C he fitted and a cargo compartment for tools and cables. And it's not powered by an SL engine because "that'd be crazy expensive," according to Leno. Instead, power comes from a 1980s Mercedes truck engine. And because Jay's a good guy, he added a small decal on the door, signifying that his truck isn't the real McCoy. But the best part of this video is Leno's demonstration of what it's like to drive. Check it out.