I used to tow motorcycles with my 2008 grand prix somewhat regularly. If we assume each moto is 430lbs, the open trailer at 400, and another 500 in gear we are talking over 1500 lbs. I towed thousands of miles this way although most of it was highway miles and I now have 132k miles without any known issues. Some of the towing I did without a transmission cooler nor shift kit and some of it was with both.

From the discussions I've had, some generations of the transmission do NOT have a hardened 4th gear hub and are more likely to fail (so tow in 3rd). I'd recommend checking that you have fresh fluid, a transmission cooler which helps the temps significantly, a shift kit, and driving without cruise control if you are in hilly areas or you find the trans shifting a lot (you can better keep the trans from shifting with your foot).

As others have said, watch your total weight, the tongue weight/balance of the trailer, and just take it easy. If you trans has any issues I'd stay away from towing.