After that, the race was on.
By Friday morning, there were tweets from the three other automakers—but one campaign has gone further than others.
Ram took its efforts to win Fallon over from the information highway to the streets of New York. The company parked a 2014 Ram 1500 Crew Cab outside 30 Rockefeller Center—where the NBC show is taped—with a sign that said, "Big Enough, Jimmy? Test it out."
Fallon mentioned the Ram during Thursday night's show, and even sent a member of The Roots, the show's band, to test drive the truck.
So is Fallon serious about buying a new truck?
A representative of the "Tonight Show" said he has made no plans to announce buying a pickup. But that probably won't stop automakers from trying to win him over. And if one of them succeeds, you can bet they'll send the host one of his famous thank you notes.
Disclosure: NBC is owned by CNBC parent company NBCUniversal.
—By CNBC's Phil LeBeau. Follow him on Twitter
Questions? Comments? BehindTheWheel@cnbc.com.