If you haven't pulled the door card before, then you probably don't know that the Titan window regulator assembly is quite a bit different from what most look like. Most use a continuous braided wire, unsheathed, that is looped around a couple of pulleys with a motor stuck in the works kind of like an old 8 track tape. Nissan uses braided wire inside of sheaths.....and they rust up and fray inside the sheathing....and the overall design is a bit 'different' from the norm. It's not wrong, but in my opinion it can go bad in more ways than the more orthodox regulator design and is therefore more difficult to diagnose. Here's a couple of image views to see what I'm talking about....
Mercedes regulator: http://cdn3.volusion.com/autc2.bj7vj/v/vspfiles/photos/EMB2107301646-2.jpg
Titan regulator: http://www.partsgeek.com/assets/dimage/full/1313518.jpg
This window problem is an old one within this forum with a lot of posts about it.... and there are only a few that seem to have found a solution...everything from bad switches to failed motors. Here's a way to diagnose where you might have a problem that can be addressed, Remove the entire track and motor from the door then remove the motor from the regulator. First hook just the motor back to the wiring harness and make sure that the motor will turn freely without any load. If not, then put a multimeter to the connector, depress the switch to activate without the motor attached to check the switch for continuity/voltage. If good, then the motor is shot. If both are good, .....take a socket wrench and put it in the back of the regulator and turn it in each direction and check the cables to make certain the cables look good and it goes back and forth without much effort.......if not good, then replace.
One final thing I can offer, is that there are dry silicone lubricants that don't change viscosity from temperature changes and don't attract moisture.....they are a good thing to use on the regulator moving connections, hinges and in the window tracks. As a last resort before you spend the big bucks on suspect parts... give your motor a mild whack with the handle of a screwdriver. For some reason, it has resurrected more than one motor that was failing.