We have used ours in the middle of summer in both San Antonio and Arlington. The single AC won't keep it 70 in there, but the only time that it even got up towards 80 inside is when people were going in and out a lot. We found that if we closed the door to the garage and then opened the main AC vent in the living room it kept it comfortable inside. Nice and cool at night.
Ours has the built in Onan 4000, which is I believe what they came with if ordered from the factory. Not sure that going to a 5500 would be of any help, since the trailer is still only wired for 30 amps input into the electrical system. There is a fairly good chance that if you added the 5500 and then tried to run 2 ACs you would still be tripping the main breaker or doing some other electrical damage. Not sure on this, confirm with someone who knows more about these then I do.
Our local dealer has told us that they can add a second AC for about $1000. This AC would be run with a normal 20 amp cord that we can plug into the 20a outlet on the post while at RV parks. This would bypass the 30A main feed line and definitely allow the second AC to run. He also said that when boondocking we could plug this into one of the exterior outlets on the camper and the 4000 genny would "probably" run it without tripping anything, as long as we were careful about microwave, hair dryer, etc...
Ours has the Rocky Mountain package, which I was told means more/better insulation. That may be complete BS from a guy trying to sell a camper, but it does have the sticker on the side saying that it has that package. Maybe that is why, but so far it has never gotten hot enough in the camper for us to decide to spend the grand.
Sorry about being long winded, hope it helps!!
2006 Chevrolet Silverado 2500HD CCSB Duramax/Allison
2012 Puma Unleashed 356QLB FWTH