I'm not quite sure who taught you how to analyze investments or calculate pmts but....
a 60k note spread out evenly over 6 years at 3% has a pmt of $911.62
($911.62 x 72) = $65,636.64
and that's at a used car rate
a 60k note, 6 yr term, 0% finc has pmt of $833.33
If you have 60k and you want to purchase a new vehicle, it would be foolish to pay 60k cash for a vehicle when you could finance over 6yrs and the sum of your payments still be 60k.
Instead of putting the 60K down on the truck, I can finance the truck, and then I can invest that 60k in a fund, for example purposes, that returns 10%.
That 60k that I invested (instead of paying off the truck) is now making me 6 grand profit (60k x 10%) per year. I can apply this 6k to my annual truck payment. At $833.33/ month truck payment equals 10k per year. This means that after I apply the 6k, I will only owe 4k per year on this 60k truck.
Any time your cost of capital (in this case - the finance charge, which equals 0%) is less than the return I can get elsewhere (investing in a fund that returns 10%, for example), you should extend the term of your note for as long as they will allow!!!!
With this example, which is absolutely feasible, I would have only paid 4k annually out of pocket over 6 years = 24k for a vehicle==> that's worth around 30K come trade in time