Though no one answered my question directly, I tried the app and it says that with a 2007 Chevrolet 2500 HD 6.6L LBZ, I can tow 1,700 lbs with a 5th wheel. I tried it three or four times.
Wow! I am WAAAYYY over that! ;)
On the CDL question. I am not over 26,001, but I do already have a Class A CDL. I have had one for years as I used to drive commercially.
I can't answer the question about the Texas driving test, but as far as "driving" goes. If you are simply pulling a 5th wheel or trailer to do the test you will probably be all right. With some semis you have a more difficult time as the axles are further back increasing the "off tracking". It's been a while since I have taken the tests. It seems like I might have had the most difficult time with air brakes on the written, but can't rightly remember.
If you have towed trailers in your life then you will do alright. Find an empty lot and use caution cones to practice the maneuvers and you will do fine!
