2006 Chevy Silverado 2500HD, Allison, Duarmax 6.6L:
Put 24 gals of gas into the tank that still had about 1.5 gals of diesel remaining.
Drove 9 miles. Other that a slight increase in diesel noise everything seemed OK. Parked it and shut it down.

Returned to truck 2 hours later, would not restart. Tried 3 times, then flashed back to image of the pump and realized I grabbed the wrong nozzle.
Smelling the filler spout confirmed the error. Embarrassing tow truck ride home.

Fixed it by:
Used a siphon pump and several gas containers to empty tank.
Replaced fuel filter.
Added 5 gals diesel.
When priming filter, I kept pumping until only diesel came out the bleeder port.
Caught overflow in a drain pan.

Ready to try starting. Figured I'd give it 3 tries for 10 secs each.
First and second tries did nothing but crank the engine and further purge the fuel lines.
On the third try it fired up, ran erratic for about 10 secs, then smoothed right out.

Drove to gas station filled it with diesel and normal engine sounds and exhaust smell returned. All seems to be fine now.
Phew!

My gardener just scored 25 gals of free lawnmower gas with a little diesel fuel additive.