[kevinr1970]

Do your research on other trucks like yours (PS, there is a shorty for sale on this site just recently for I believe $5500 or $6500). Look on Autotrader, classic car Trader, Craigslist, etc. Print the ads out so you have records even if the ads go away.
Don't be foolish and show thaem ads for "show" trucks and try to use that as leverage as they are not stupid. But do find as many "like" vehicles as you can.

Don't even talk about a "buy-back" from them as in your opinion the amount to repair the truck doesn't exceed the value (the amount it will take you to replace the truck).

I would call the adjuster today and tell him:
"About that rental car, I thought this would be a simple deal and we would have settled by now. Since this is going to drag on for a while I need to get a rental and it needs to be a full size truck, like the vehicle your insured damaged."
Don't mention anything about your other cars as that has nothing to do with this. You need a full size truck and and yours is down for now.
Do you use your truck for business? Even better as you can't conduct business in the truck with the dents in it. Although I would be carefull with that one. If your not paying the insurance as a "business" vehicle that may bite you in the hieny.
The rental car starts to ad up real quick and encourages them to make a fair offer.