Electrical problems are difficult to find but not impossible. A few thoughts:
1) With the truck running, measure the volts of your battery with a voltmeter. Given the alternatotor will be running as well, the battery should stay at bout 13+ volts. If it drops while doinng this test, I would question why the dealer believes the charging system is okay and point this out to them.
2) Has the dealer monitored the battery during the day to see if power has been called when the key is not in the ignition? You mentioned the dash lights stay on when you turn off the truck - how long do they stay on? If for a minute or 2, that itself should not drain a decent battery. These and other electrical devices may be staying on longer - the tough part is finding them.
3) Do you have any electrical mods in the truck (navigation, lights, stereo, winch hook-up, etc.) that may be on and you are not aware of? Check out any toggle switches or open-end wires under the dash or under the hood. You may find the problem just by seeing something that looks wrong. If you find any of these things, measure if any amps/volts are coming through with a simple 12v reader you can pick-up at any auto store.
4) The dealer should make you whole in any event but since I am a do-it-yourselfer when dealers say things that do not seem to make a lot of sense, I would do the above too.