Drain the tank and filter replace with fresh diesel and some 2 cycle oil.
Start the truck and use it the way you have in the past.
Gasoline will not damage the engine,if the gas concentration gets to high the engine will stop running because it wasn't designed to run on gas.
About the only damage that could happen would be to the pumps and injectors from the gas being very dry.But for the short amount of time the gas would have been in the system,don't worry about it.
90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews