You can't tow very well with a low ratio fuel economy axle. It should be a 3.73 ratio at minimum, and a 4.10 if the engine doesn't have a lot of kick. Eight cylinders are better than six. It's good to start with a strong drivetrain.
Trailer tongue weight easily is 150-300# higher than empty tongue weight (considering modest personal gear in trailer. Filled propane tanks and WD/antisway gear is all mounted up front). Add up anybody and anything else in the tow vehicle. If that and tongue weight doesn't exceed TV payload capacity you're almost good to go. This assumes one is doing no tricks to lessen tongue weight by back-weighting the trailer (a very dangerous, unstable proposition). Because then I am going to state -- with a normal loaded trailer with which you don't exceed TV payload capacity, you will not be exceeding the tow capacity. At least I've never seen it.
Maximum tow capacity is just that - maximum. It's figured under highly unlikely circumstances of a lightweight driver, a quart of gasoline (almost) and absolutely nothing else in the tow vehicle. Then you can load that tongue weight to the max. It always looks good to have high tow capacity in the ads, so the advertising dept puts in some fudge factor too. Whatever... The tow capacity number circumstances are never seen in the real world. So I stand by my statement at the end of the last paragraph if you're going to be towing with relatively normal usage.
That being said, for a truck or SUV you already own you might check kbb.com or edmunds.com, used vehicles and look for specs. New vehicle tow capacity should be on the mfgr's website.