I pull probably 5k pounds fairly regularly... probably 10-15 times a year. Can't offer much more advice that hasn't already been given, but I WILL empasize everything that's been saida bove & elaborate on it a little more
ABSOLUTELY get the air bag 1000 kit. Dirt cheap and a huge help I generally run about 35psi in mine but experiment and see what you like. Ride SIGNIFICANTLY improved even when NOT towing.
ABSOLUTELY get a weight distributing hitch if tongue weight approaches the 600lb mark and/or causes your rear end to drop an inch or more WITH the airbags. The one I got is branded as a Nissan OEM set-up. Not sure who the actual manufacturer is though.
http://www.thenissanpath.com/viewtopic. ... stributing
(Don't bother looking on 1stAAANissanParts.com. It's not that cheap on there. The link I give is cheaper)
ABSOLUTELY watch your transmission temperature with some sort of a gauge. I got myself a Bully Dog GT tuner and love it. I've also gotten my transmission temps as high as 250 degrees so you're definitely going to want to change your ATF more frequently (I'm changing mine about every 30-40k miles).
ABSOLUTELY spend the money on a good brake controller. I use a Tekonsha Prodigy. Works great.
Also, be sure to get a proper drop hitch. My trailer's tongue (a typical cargo trailer) is significantly lower than the reciever on the back, which is farily high for a stock SUV so I had to go with a 9 inch drop. Getting your trailer fairly close to level is important.
here's the drop hitch I ended up going with.
http://www.amazon.com/gp/product/B001EO ... UTF8&psc=1