Wow 55,000 miles? That's not even broken in yet! LOL I don't know all the values but I know on a ScanGauge 2 from what I've been reading key on engine off should be between 0 and 15% for the IPR and on a warm idle should be between 22 and 24 percent. Outside of those two parameters I have no idea what's normal. Today I am actually shooting video of my IPR and ICP numbers on my ScanGauge to see if I have anything I need to diagnose as far as a high pressure oil leak.

Now beyond that two simple things you could do to check that could cause a surge is on the right valve cover is your ICP sensor, and you can unplug that and look at it and make sure it has the little white clip that's effectively a spacer on that plug, and that it's not saturated in oil or that the wires are damaged. On the driver's side to the right of the valve cover is a little stem sticking up that is your exhaust back pressure gauge or EBP and it has the same type of pigtail and plug, and it should also have the white spacer in it. Those are two areas I know that if they're not reading correctly could cause surging issues, which I have had in my truck sitting at idle as well. It's really fun when it decides to Surge when you're really close to the car in front of you if you're not holding down to the break really really well. I just got done replacing my engine wire harness and my IPR was replaced 6 months ago and I replace an injector and did a bunch of other work and right now I don't have the surging issue but I have no idea what fixed it. I also have a 2005 truck.

 

Unplug the ICP sensor on the passenger side valve cover and see what happens. If its showing oil at the plug, replace the sensor and don't loose the little plastic clip that goes in the plug. Won't hurt anything, clear the code later, should fix the issue or show you what to fix. Then start using a good synthetic 5W-40 oil.