How much more will it weigh? I suspect you are still OK. But getting close to the limits of the truck.

That 2h trailer will probably be 14,000lbs. The diesel version of that truck are rated for 15000 - 16000k total trailer weight. But the pin weight will also come into play. Especially on a 3/4 ton truck. You may be fine for the overall trailer weight, but too heavy for your trucks pin weight.

Pull up the specs on the gas engine 2500 and see what it's rated for.

If you're thinking of a notable trailer with a 10' LQ that's 8' wide and 7 1/2' high, you will probably be close to or exceed the truck's rear axle and tire capacities. The weights of trailers can vary greatly, depending on the brand, material selection, overall size and installed equipment. A half a dozen manufacturers of 24' trailers, will all have different specifications and weights. A trailer's length will not be the only determining factor of its weight.

Your terrain in southern IL is fairly level and you may be able to get away with the small gas engine. Any type of hills will quickly test its mettle. In our part of the country, it would be badly insufficient. You are not experiencing any difficulty with power now, so most of your travels must be on fairly level runs. The new trailer should not pull significantly different than the one you have now, on those same types of roads.

To know if your truck will haul a specific larger trailer, you have to know the truck's specifications and the pin weight of the new, fully equipped trailer with a load. If you are purchasing the same brand and equipped trailer, you may be able to extrapolate a reasonable guess for the new weight, using the manufacture's specifications. However, unless that trailer manufacturer installs its own LQs, the combined weights of two different companies may be erroneous.

Gard

That seems awfully high. Are you sure you aren't confusing the GVWR of such a trailer with it's base weight? The GVWR is the weight of the trailer when its been loaded to its maximum capacity. The base weight is what it weighs before you load it with your horses and gear.

I am assuming a loaded trailer, bare trailer, LQ,  gear and two horses.

My 4h  8' LQ was right around 16,000 lbs loaded.  different makes of trailers will be heavier or lighter depending on how they are built, width, height, materials, options such as water tanks, awnings, mangers, hay racks, generators etc.

A plain jane, no LQ gooseneck trailer with a 24' box is going to run 6000lbs +/-

It really doesn't matter what it weighs empty. Nobody buys a trailer to pull empty.  The concern is what will it weigh loaded and hooked up to the truck.

Just a word of warning,  do not believe what auto dealers and horse trailer dealers tell you.  Double check both what your vehicle can pull and what a trailer weighs. 

 I learned this the hard way when I bought a truck a few years back. The dealer told me it could pull a trailer much heavier than it was actually rated for. I've also been given some pretty light weights from trailer dealers only to go to the manufacterer's sites and seen that they were much heavier that I had been told.

 The dealer can tweak the PCM and give you 5 or 10 more horsepower. You'll never notice the difference, other than the engine spark knock, having to use premium gasoline, poor mileage, etc. etc.... "Westers" can reprogram your PCM, that is, if you want to go drag racing, so can a, "Wait-for-me" tune...  Not much you can do to a 6.0 gasser for more power without some serious engine modificationssuch as a performance camshaft, cylinder heads, forced induction, etc.  If you had a Duramax diesel, you would have more than enough power for that trailer already. Does your truck have 3.73 or 4.10 gears?

The two best GM truck tuners out there...

http://westers_garage.eidnet.org/

http://www.wait4meperformance.com/