There are two aspects to towing:
1) Are you within the specified weight limits of your specific truck. For your specific truck, One must stay within the GVW (how much just the truck weighs all loaded up and hooked to the boat), the GCVW (How much the whole rig weighs, boat and truck all loaded up), and The TW (tongue weight of the boat)..
2) How comfortable is it to drive. IMHO here is where a diesel makes a difference.
Oddly elnuff, given the same exact same truck (in gas and diesel) staying within weight specs, the gas can tow more. The added weight of the diesel adds to the base weight of the truck and eats up GVW and GCVW thereby reducing the amount of payload ortrailer that can be carried and still stay within limits of truck.
Be careful reading the advertised trowing specs in brochures. They are based on a regular cab, stripped down vehicle. Every option that is added to the vehice (4 wd, diesel, etc.) subtraccts from the carrying capacitty of the truck. One must look at the sticker on the pillar of the drivers door to determine the numbers for your specific truck.