I have a 2009 Cadillac CTS, it has 46K miles on it and has recently developed a slightly rough-lets call it a vibration (felt through the steering wheel and thru the gas peddle) when the car is warm, at about 2K RPMs and mostly at about 70 to 75 MPH(there are times when its there all the time but not often). No codes are given thru Onstar and no lights are lite on the dash. The dealer, of course, counldn’t duplicate the problem, they checked for software updates but there were none. I first noticed it while I was driving at about 72 mph,on the highway, and all of a sudden I went from having a nice smooth ride to feeling this low rough vibration. I only have 4k miles before the warranty is up so if anyone has any ideas let me know. Thanx
Could you clarify…is it related to the engine speed or the car’s speed?
Maybe the dealer’s mechanic didn’t want to exceed the legal speed limit by 5 to 15 MPH (or more)to duplicate the problem.
How many miles on the tires? This sounds like a wheel balance or tire issue.
?? plenty of 70mph freeways…
But that’s still over the speed limit. I just couldn’t resist the tweak. 
Maybe your car needs to be aligned. If you drive over speed humps, railroad crossings, or pot holes at a good clip, it could mess the alignment up. It can still track straight and be out of alignment.
Are you really sure the vibe comes through the gas pedal? That suggests an engine mount issue.Otherwise I would think its a tire or alignment problem.
Front alignment problems can have brake pedal pulsation as a symptom.