I agree. I've walked in your same shoes and had the same experience with the 660.
And on a side note, (not directed specifically at you, CJM8515) as other have stated, the 660 is not great on 3/4 ton and up diesel trucks. Well, there is a reason why those trucks come with two batteries from the factory.... because they need more than one battery. And they need more than one jump pack, too.
Most guys in the jump start business carry at least two JNC660's. (I did anyway. In fact, I still do) All you need to do is put one JNC660 on each battery and most of the time the diesel truck will eventually start. I say "most of the time" because diesel trucks can have other problems when it's cold outside, besides dead batteries. All the jump starting power in the world isn't going to fix gelled fuel. If the truck won't start STRICTLY because the batteries are low, and the truck has no other problems, two JNC660 jump packs on a truck with two batteries will usually get the truck started.