Please take your time or you will loose thousands and end up purchasing the wrong tow vehicle.
1. Most important. Learn what the "true" towing capacity of any vehicle your looking to buy. Pin weight and so on.
2. I Highly recommend purchasing a vehicle from an auto broker or Triple AAA. You can get the same warranty as any dealer will offer and save thousands of dollars. Ask your credit union if they have a auto broker they work with. AAA will give you a price in minutes to compare against any dealer. For example: A few years ago my neighbor purchased a Chev Derimax Diesel 2500 top of the line for $46,000. If he would of gone to the local auto broker he could of got the exact same truck for $36,000 to $38,000. He was in a hurry and or just didn't want to listen to me.
3. Check and see if Dick Smith's Motors in Kellogg, Idaho is still saling trucks and cars. He once was the number one Dealer in the nation because they would sale approximately 120,000 vehicles per year at the lowest cost of any dealer in the nation. Basically gives you a price on line and you will know in a few minute what you will be saving.
Sorry, I don't have the time to give you more details for now. maybe latter.
PS: Please forgive my writing skills.