The tractor may weigh more than you think. My JD 770 is listed at around 2,150 lbs. Actual weight with a Front End Loader, liquid filled rear tires, and a 4' bush hog plus fuel, is around 3,500 -3,700 lbs. Add the weight of the trailer, which may run 1,600 - 2,000 lbs, depending on how heavy duty it is and you're probably over the 5,000 lb capacity.
You need to know the GVWR (Gross Vehicle Weight Rating) and the CGVWR rating (Combined Gross Vehicle Weight Rating) (which should be posted on your driver's door jam). The GVWR is the van, passengers and stuff. The GCVWR is the Van, you, tools and "stuff" in the van plus the trailer.
Look at these numbers as examples. They may be close to actual for your vehicle. Say you have a 4,400 lb van with a GVWR of 6,100 lbs and a CGVWR of 10,000 lbs. With just a 200 lb driver, you could tow the 5,000 lb trailer and only have a total weight of (4,400 + 200 + 5000) 9,600 lbs. No problem with the 10,000 lb GCVWR. Load the Van to it's 6,100 lb capacity and you can only tow 3,900 lbs and not exceed the GCVWR of 10,000 lbs. If you go fully loaded with a 5,00 lb trailer and a 6,100 lb van, your way over a safe load.
If you look at the hitch platform, usually near the receiver, it should have a weight rating. On my Jeep Cherokee which is rated to tow 5,000 lbs, the hitch says 2,000 lb max without a weight distributio hitch, 5,000 with. A weight distribution hitch puts one third of the tongue weight on the front, rear and trailer axles. Otherwise, you would have 600 - 700 lbs on the hitch ball, seriously lightening the load on the steering tires on the van.
Also keep in mind that for every 1,000 ft elevation increase, a gasoline engines loses 3 - 4% of its power, so while these maximum tow ratings work at sea level, (your rig doesn't weight any more a 5,000 feet), but it's power is down to 80 or 85%.
A weight distribution hitch is critical for your application, and possible a sway control on the trailer as well. I saw a Nissan pickup with a 4 wheel car trailer towing a Honda Accord in the rain. It had jacknifed. A frame equalizing hitch would make that rig much more stable as well as keeping more weight on the tow vehicle steering wheels. An anti sway control on the trailer would also have helped prevent the problem.
A heavy overload on your tow vehicle may shorten the service life of your vehicle, will accelerate tire wear, could cause a heat relateed tire sidewall blowout and in the event of an accident may increase your personal liability.
If you do decide to do this. Know the actual GCVWR and GVWR. Weight the tow vehicle loaded as it will be used and the trailer and tractor ready for the road at a commercial scale. As already mentioned, do not tow in Overdrive, your transmission will hunt between gears, overheat and fail. Keep tires on van and trailer inflated to their maximum rating. While you have a transmission cooler installed, it's sized for the GCVWR of your light duty van. If you exceed that weight, the cooler will help, but may not be enough.
Bottom line, my guts tell me you will be in an overload situation, and I would recommend against it.
I know money is a concern, (it always is for everyone) but trying to tow this weight with your van may cost you a lot in the long run.
I hope this long post wasn't confusing. Good luck.
Joe
