Getting gas with long trailer?

I recently added an in bed auxiliary gas tank, but before that I never traveled without at least one five gallon gas can. When my current truck was two or three years old we were on a trip and the truck was struggling to maintain 60mph on a flat interstate. Pulled over, nothing was obviously wrong. Gas gauge was showing 1/4 tank DIC was showing somewhere around 60 miles of range. Get back on the interstate and now 50mph is max and the it dies. Luckily we were close to a rest area, coasted into there. No change in gas gauge reading. I pour the gas from the can into the tank. Truck fires up and runs like it should. Something must have caused the gauge to hang up at a 1/4 tank. Hasn't happened again since.