I would like to second (or third) driver training and incentives.
There is a company in Europe (Germany IIRC) who have focussed primarly on the drivers and have had huge savings.
The other thing would be considering setting a company speed limit, the company who I last drove for had a company speed limit of 80 km/h instead of 90 km/h, that saved them fuel and it was marketed as being for safety, there are numerous companies who have done the same.
Not sure how your company runs, but try and branch out and if your wagons return empty, try and find 'return loads', it wont be a fuel saving but if you have a truck going empty from A to B, and can get a return load, it helps the bank balance. Just make sure that it is a good simple run.
Longer term, consider buying low rolling resistant tyres. Super singles help but as you said conditions may not be right.
Longer term there are (at least in Europe) axels that have been designed with efficiency in mind.
Again longer term - investigate the posibilities of teardrop bodies here is an English company who produce them
Aerodynamic Teardrop Trailer
And another long term consider the purchase of alternative trucks, many of the European brands are keen to get out into the rest of the world, and presumably offer a good deals.