Allison troubles

[eggtrucks]

We have two identical straight trucks, 2012 Peterbilt 348 with Paccar PX8, with Allison transmissions. The one runs great, the other one has gone downhill in regards to its shifting. It will shift up to the next higher gear way to soon. Example coming into a hill with the throttle all the way down, it will shift from 3rd to 4th at 14-1600 rpm, same from 5th to 6th. (Its a 6 speed), and feels like its not even trying to pull...when rpm drops to maybe 12-1300 it will downshift a gear, and will pull decent until 14-1500, them shifts up, and then we start losing speed again.
With 6000 lbs loaded any moderate hill, it will only go 30-40 mph up the hill. The other truck(thats working properly) has no probllem pulling 50-60 the same grade.
Had it to the allison dealer and they replaced speed sensor and wiring from sensor up to the tcm, and undated the software. That didnt help a thing. I swapped tcm with the other truck, still no difference. Replaced trans filter and fluid, no help.
Did fuel rail leak test, thats good, turbo boost is good, monitored fuel rail psi vs commanded. No problem there.
Any ideas while its acting like this? If use the button to manually shift, it has plenty of power...Not sure where to turn next....