Add me to those who had it done at Cummins for around $400. I had my torque increased to 1150 last year. No warranty problems.
I had mine done at Cummins Jacksonville, FL. Any Freightliner truck dealer who is Cummins certified can do it. It's all done with software.
You need to explain you are not looking for an uprating but an upgrade.
If you search here for about a 1 1/2 years back on Cummins L9 torque increase or something like that, you should be able to find the Cummins reference number and how to get them to do it.
I wasn't challenged when I explained I wanted to have a retune from RV to trash truck. This is actually what this upgrade sets the parameters to be and why it feels snappier on acceleration. Trash truck are heavy to start etc. The reprogramming also changes transmission shift parameters.
It's all good and worth the money although totally unnecessary. But who says toys are necessary