For the trailer in question, any of the 2500/3500, 250/350 trucks will do it. Gas motors will be fine at that weight, just make sure the axle ratio is correct for the proper gcwr for the truck and trailer combo, which is what the max the truck and trailer should weigh as spec'd by the truck manufacture.
IF you decide to buy a new truck, and decide diesel is the way to go, try to find a 3500/350 SRW if possible. It will give a little more payload over the 2500/250 diesels. That way if you decide to step up to a 5ver in the future with the current truck, you probably will be ok pending the size of the 5ver. Most diesel 2500/250's run out of payload when towing a 5ver unless it is fairly small.
Keep us posted!