How long a trailer and be comfortable towing on a long trip

Of course you realize why a SALESMAN would be telling you this, right?

Truthfully you probably won't be able to tow much longer than you already have due to the weight of the trailer, as others have said. 7000lbs in my opinion is really pushing the limits of most 1500 pickups as far as over-the-road comfort goes. You can play the numbers game and tow more, but after the fascination of the new trailer wears off, you will realize that it just doesn't feel all that good going down the road.