^ sticking to the torque curve is the best way to deal with it. Some people say that towing in overdrive is ill-advised but if Nissan (documentation, not the dealer) give it the ok then go for it - but you need to find that sweet spot.
As an example: the 126kW YD25 engine's torque starts climbing around 1400rpm and finishes its steep climb around the 1900rpm mark. Sitting anywhere from 1800-2000rpm provides the most torque for the least amount of fuel, but you have to balance that with wind resistance - the faster you go, the harder to push through the air and the more fuel you'll use (the dyno NEVER shows how that works!). Staying near the bottom of the envelope is the most efficient and in my car that's around 85km/h (when towing 2.5T, we last returned from Grafton using 17.4LPHK but that was with a faulty turbo boost control solenoid).
Just a note on the torque curve - you don't get a lot more torque on a standard engine above 2000rpm anyway - check the dyno chart below (lifted from dynomotive's web site flogging the Unichip diesel power chip). The torque is basically all done and dusted by 2000rpm and starts to fall away at higher revs (which also means higher road speeds). The horsepower curve (marked "standard power") peaks around 3400rpm with very minor changes through to 3900rpm. You're using serious amounts of fuel at those revs.
The chip (just to highlight what it's doing for the $ invested) has brought a modest increase in torque which peaks only a little earlier and a nice increase in horsepower, with a peak at lower revs than standard. Not moving the peak torque point by much is clever and highly desied, because in top gear those RPM represent a particular road 'cruising' speed that you really want to be sitting around (especially when towing) and making that too low means you're going slower.