I have the same issue with my 2006. I just replaced the pads front and rear recently and did clean up the pistons a bit. It was so hot on the rear I ended up taking a laser temperature sensor with me. Over 150 degrees without using brake in the rear at all. I can barely spin mine rear wheel on the center stand.
I took the rear wheel back off, removed the caliper and looked. It seems like the center piston that is linked to the front is not retracting all the way. I pushed it in, put it back together and the wheel would spin way freer than it was. But then after a ride, the rear is dragging again.
I too have pretty full fluid on both front and rear (this is all new stuff to me). I'm wondering if there is something else that needs to be bled a bit to reduce pressure?
