Is this a new truck or a used truck? Either way, use Edmunds and KBB to price it out. The size of the dealer really doesn't make any difference, except that they may not have enough sales volume to accept small profit margins on a given sale. They may not be able to afford giving you a fantastic deal that you might be able to get at a bigger dealer.
For a used truck, you want to pay approximately what those sites list as "private party sale" price. Wholesale is about what the dealer paid for it, and "dealer list" is the high end where the dealer starts negotiating. Also use other dealer advertisements as a comparison for "dealer list", and Carmax is another good benchmark for what you'd actually pay.
For a new truck, you want to start negotiating around what Edmunds and KBB say is the invoice price (including the destination charge). If there is a cash rebate, subtract the rebate from that price. Always negotiate using a number - don't ever say the word "invoice" or something like "invoice plus $x" to a dealer.