It must be the idling. My friend and I had the same trucks T680 doing the same loads in the hills of PA. He was getting 9's and I was around 7-7.5 but I am a far more aggressive driver than he is.
I rolled up on him in PA and hollered on the radio, "hey. company name why in the **** are you holding up traffic?" (we where the only ones on the road for miles.)
He said "what?"
I hit the interior light and flipped him the bird as I passed him with a smile.