My first truck, many years ago, was a 79 K10. It had dual tanks, which I thought was a cool feature at the time.
This was before pay at the pump and debit cards, so filling both tanks meant the clerk was inside, phone in hand, ready to call 911 every time I left the pump to fill the other side. Or I had to go in, guess the amount and pay cash up front.
Anyway, it was a Christmas eve and I was driving my wife 300 miles to see her parents. No issues on the way up. Coming back the next evening, in a blizzard, I went to switch tanks. Uh oh, the switchie no workie. The switching valve, whether frozen or junk, had failed. 16 gallons of fuel @ 10mpg= less than 300 miles. Back then, on Christmas Day night, most gas stations were closed.
Me, not being as dumb as I look, had two 5 gallon jugs of fuel in the bed for just such an event.
I currently have an 80 K15 with dual tanks under restoration now. My druthers are to keep and run on one tank until I figure out a larger one tank solution.