Late reading your story and glad it seems to be working out ok and your truck is getting fixed. I too have a steep driveway downhill that is tricky in snow and ice. Wanted to echo Tikki2's recommendation to use neutral. This lets the antilock brake computer prevent the spin you experienced. When a 4x4 dually is empty there is a huge mismatch in traction between the front and rear but with the trans in gear they are locked together. In neutral the computer can apply brakes independently to prevent this most of the time. It can really help.
