I've a 2012 Limited 3.6, 500 mi. I get the pulsation (the rpms stay steady) as you mention right around 60 on slight or moderate grades as well, that increases in frequency up through 70. I've had it checked by the dealer who while unable to reproduce it, claims it's torque converter lockup, and it's a design characteristic of the vehicle due to gas mileage compromises, etc. There were no outstanding TSBs for my vehicle nor was it throwing any error codes. It was also described as related to 'ECO' mode, and going heavy on the accelerator and getting the car out of ECO mode should alleviate the problem - however, this didn't work - the problem occurs when I'm heavy on the throttle as well. I'm also rejecting the description that this occurs when I put the vehicle in a specific 'condition'; driving up a normal hill on the highway at nominal highway speeds isn't what I consider a 'condition' (I'm not exactly hammering the vehicle up Pike's Peak in a road rally. I've also read that under mountain driving conditions you should employ tow/haul mode (alas, I don't have that button/package)).
I believe this might also be described as on the forum as transmission shudder, but could be wrong on this, as I've not been in another GC other than the one I have.
Whatever the cause - on a 40K$ vehicle, with 290hp - this should not be happening - no engineering team would possibly foist this sort of design/compromise on the public.
There is at least one TSB for 2011 models for 'transmission shudder' requiring a software update that I've read varying reports in the forum here that ameliorates the problem, but doesn't resolutely solve it. The TSB is not applicable to my vehicle - I'm guessing my build date includes the updated software. Poking around the internet there's a lot of data that is being processed by the whole drive train system (pedal pressure, temperature, etc) so I'd imagine it's not quite so easy to get the software right for this given the electronic and mechanical components. Easy or not, it needs to be fixed.
This link ( http://www.wk2jeeps.com/wk2_transm.htm
) is interesting about the transmissions in general (including the upcoming 8 speed tranmission that is described as fitting in the existing housing, so that may be the ultimate solution).
In any event - I'll be pursuing this issue pretty aggressively and will be having a drive with the technicians to demonstrate exactly how to reproduce the issue and ensure that they can reproduce it as well. We'll see if they start replacing drivetrain components.
Good luck to us all.