Stumbling after start up

[Big Moose]

Had a similar issue on one of our trucks. Sometimes it did it and sometimes it was good. When it was stumbling the truck would vibrate. Are you able to tell from your live data on your scanner if some cylinders are misfiring? On ours, one side (bank2) was showing a lot of misfires. The front O2 sensor was showing different voltage readings than all the others. Pulled it out and it was really black. Put a new one in and still did the same thing. But I had previously pulled the spark plugs and noticed they were really black as well on that bank. So I decided take it for a good hard drive to see if the plugs would clear themselves off. Well, didn't have to drive to far to accomplish that. Truck runs so smooth now, issue fixed.

What I'd recommend is pulling your plugs and inspecting them, that should tell you something.
One other thing to note, 42 psi is to low, should be around 52 minimum with the return type fuel system, it could be you're starving a little bit. it could also be that the strainer on the fuel pump is plugged or the inline filter.
Good luck