You better believe it!
If you have a recent model, therefore common rail, diesel, running any amount of gasoline through it is potentially a major repair. I've a BMW X5 diesel, and have seen instances of folks making that mistake, and being given estimates of around $15,000. Your truck may be cheaper, maybe only $10,000. But don't count on it.
Here's the deal. If you (or somebody else, for that matter) pumps gasoline into your diesel ride, DON'T START THE ENGINE. It is going to cost you a few hundred bucks because the contaminated fuel has to be disposed of as hazardous waste. But all they have to do is drain your tank and refill with good diesel. If you so much as start the engine, they will have to do that plus replace the fuel filter and flush the entire fuel system, thereby doubling the cost. If you run the vehicle at all, you may have to replace the fuel tank, fuel lines, fuel pump, high pressure fuel pump, and all the injectors. The reason is that gasoline does not lubricate the HPFP, so it will grind itself to death in an increasing death spiral, in the process distributing microscopic metal chips everywhere, chips that cannot be reliably flushed out, and that will cause a new HPFP to distruct in short order.
Be careful out there, folks. NEVER let anybody with the smell of gasoline on their breath anyplace near your fuel filler.