Tow rating is more sophisticated than "not more than 75%". It's on your vehicles sticker. Take the GVWR (gross VEHICLE weight rating) and subtract it from the GCWR (gross COMBINED weight rating), and that is your tow capacity. That is completely different than your tongue weight rating (physical weight pushing down on your ball mount). You can find that number in places like the Trailer Life magazine tow guide (online, organized by model year).
Personally...I'll never tow with a gasser, OR with a half ton truck. Suspensions are too soft, frames are relatively flimsy, brakes are weak, transmissions aren't rated for it, and engine power is lower. My 3/4 ton does everything I need it to do - Cummins, 6 speed manual, 4x4, 8' bed, Class V hitch, trailer brake controller. I get 20mpg around town (empty or full); I got 18 mpg towing my Charger from FL to MD. It pulls my 26' enclosed car hauler like it's nothing - and I live on top of a mountain. ABSOLUTELY use weight distrubution when you tow. Worth its weight in gold. My truck doesn't sag an inch when I have my trailer hooked up because of the weight distribution setup. Before I hook up the bars? It sags about 5". makes a YUGE difference, and the truck drives/steers much better as well.
Right tool for the job, saves a ton of headaches.