High Boost Pressure

[nic670]

I use an '05 F-350 6.0l as a work truck. It has 50,000 miles on it and i recently noticed an increase in boost pressure for no apparent reason. It has usually cruised at about 7-9 psi and was extremely difficult to hit 20psi during acceleration. However, lately the average boost is around 12psi when cruising and easily gets to 20psi or greater when accelerating. Am i maybe just imaging this increase or has someone heard of this before? What could be a possible cause? Any info would be helpful. Thanks.