How can I buy a Tow truck?

Sell the Honda then use that money to buy the truck.

I'm not sure I understand your question. But you should have traded the Honda in when you bought the tow truck. When you trade in a vehicle you get wholesale (less) value for it, not retail. If you've already bought your tow truck, sell the Honda yourself and use that money to pay down the money you owe on your tow truck. Jim