Greetings Bob,
I have been where you currently are now. I towed my 25 ft. Aljo 5th wheel with my 2003 GMC Z71. 4X4 with the trailering package. When I bought my trailer, the original owner assured me that my 1/2 ton could tow it with no problem. He was correct however it was clearly a heavy load. Fully loaded, the trailer weighed in @ 7200 lbs. I found air bags a necessity. I towed that trailer over Independence Pass in Colorado albeit going about 20 mph. I eventually graduated to a 2006 GMC 2500 HD. Ironically, we are just now finishing our next upgrade to a 2013 Cyclone 3010. Again, I am at the edge of the performance for my current rig. I may find myself making the next step up for my trailer.
That is why I wanted to post here. If you keep your 1/2 ton, get a trailer that meets your weight restrictions. A gas engine is not like a diesel where you can push the envelope. I recommend air bags. An after market differential cover and a much larger tranny cooler You will need the extra fluid capacities to disapate the heat. I had noted that the paint on my original cover had been "cooked" off due to the heat I was generating while towing my 5er. Running synthetics also helps in the crank case, the tranny and the differentials.
Secondly, if you do decide to upgrade your TV, don't do what I did. For a bit more, you can get that 1 ton diesel. Even if you decide to go with a single rear wheel. I love my 2500HD, but in hind sight I am wishing I had gone with a dually. Good luck regardless!!
Jim