Towing is not all about the engine. Its also about suspension and control.
If you get a weight distributing hitch you can tow more then someone w/o.
If you get air bags like mine that mount inside the coil you can tow more. (firestone ride rite air bags ) They help with keeping the rear end from sagging under weight and boost the max tongue limit.
If you have tow haul mode you can tow more because it changes the trans shift points for better towing.
if you have electric brakes you can tow more.
Obviously if you have a bigger engine you can tow more but if the body/suspension/trailer are not setup right you can put your self and others in danger.
There are tons of factors involved in towing. BUT I Still WILL NOT EXCEED WHAT THE MANUAL SAYS!
For me, I have a 4.7 V8, Tow haul mode, Electric brake controller and Firestone ride rite air bags. That does not mean i can tow more then the listed 6800lb GVWR but it means i can tow that Max 6800lbs ALOT easier and Safer then someone else.
If i had a 3.7 V6 WK, i would do all the same things and then id say its ok to tow a 5000lb trailer but i think that might be pushing it for that engine.
Stick to the owners manual. The Ratings are there for a reason. If you dont believe that then search online or ask U Haul what they will alow you to tow with that jeep.