sorry you're in a frustrating situation. Does your van have the tow package? It should state that on your window sticker. If yes, it is rated at 3600lbs from the factory.
If no, there are aftermarket hitches made for our vans that are rated to 3500-4000lbs (here's one from Curt: https://www.curtmfg.com/part/13383
). The tow package from factory is welded directly to the beefy metal bumper so it looks to be stronger than one you'd add in later (in my opinion), however, I've used Curt aftermarket hitches before and they are a good brand. Hard to tell whether Chrysler is downplaying aftermarket hitches by saying they can only do 1500lbs because the mounting location on the van is less strong than factory OR they just want to push their factory option. After inspecting the factory tow hitch just now, I'm impressed with the structure so it may in fact be a stronger (safer) way to tow 3600lbs. While there are other features that come with the factory tow package, the most important is how the hitch attaches to the vehicle which gives it strength. You'd be best to consult with a reputable aftermarket hitch shop and see what they say about the strength of an aftermarket hitch rated for 3500lbs (like the link I enclosed above) - that shop may stand behind their assessment and installation based on how it is mounted on the van.
As for what salesmen/women tell you, that's no different from one dealer to the next (across ALL car companies, no need to single out Chrysler, though some dealers may be less slimy than others) - it sounds bad, but you have to assume sales people DON'T KNOW ANYTHING about the vehicles they sell and instead do your own research. READ the published sales literature, even read this forum. I've witnessed many sales people lie - not always maliciously, just out of ignorance.
On a side note, if your van's been in the shop so long, maybe that dealer's the problem? might not hurt to get it somewhere else for a fresh set of eyes or perhaps they have more experience