Towing my boat...RPM at 60MPH?

[dreamer2009]

I have owned my 2006 Pathfinder since new and has about 50,000 miles on it now. I have towed my other boat a bunch of times which is lighter(4000lbs) with trailer. My new boat comes out to about 5000lbs, that's boat, motor, trailer, gas, ice, and all the gear. If I am going 60, I am pulling a little less than 3000rpms with the OD off. With no boat its a little over 2000rpms OD off at 60.
Questions: Is my transmission working too hard and I will have shortened life if I use it to go more than short distances?

Whats up with the "stay under 50mph for the first 500mi of towing" as stated in the Nissan Towing guide?

Didn't see much on the search that I did.

http://www2.snapfish.com/slideshow/Albu ... =snapfish/