Steer axle weight issue

Hi guys>
I have owned a 2007 Volvo VNL 780 w/ISX. I'm having an issue that boggles the mind of myself, the Dallas Volvo dealer and various mechanics. For no apparent reason I'm having an issue with being legal on my steer axle. I've hauled many 40k loads and had no problem getting legal until recently. Loaded a trailer with a 20k, evenly loaded front to back load. My steer axle weighed at 12800. Weighed with an empty trailer and !/2 fuel full tanks and got 11880 on my steers. Bobtail weight is 11780 on my steers. Picked up a 10k load with full tanks and weighed at 12100 on my steers. In essence, it appears my steer axle has magically and for no apparent reason taken on weight that puts me close to the legal limit without a load on. All weights were done with the 5th wheel in the rear position and trailer tandems slid forward. As this issue is preventing me from my livelihood, you can only imagine my frustration. Any ideas, suggestions or direction to get ideas/suggestions would be greatly appreciated.

 

150 gal tanks x 2 @ half full. Bobtail drive axle weight is within specs (10,900 lbs). Truck was configured, 5th wheel to the rear to take max weight off steers when weighed. Thanks for the response