This is probably completely unrelated - but I figure I'll throw it out there anyways...
My 2000 5.9 has a very slight RPM jump, but ONLY while using cruise control.
At approximately 65MPH, my enging is turning a lovely 2000rpm... But when I set cruise control... The RPM's will sporadically jump up to 2100rpm and then back down to 2000rpm. This happens every few minutes.
It has done it ever since I've owned the truck (about 3-4 months now) and it's more just quirky than anything else.
It hasn't gotten any worse, and I don't use cruise control all that often, but I will be going on a long road trip in about 6 weeks and I'll probably want to use cruise a fair bit.
I can just feel the engine jumping that 100rpm and then backing off, and jumping, then backing off... At first I thought maybe it was just fighting some wind resistance or something... but that doesn't seem to be the case.