Sounds like a transmission related issue. I would take it back to the immediately if it wasn't doing that before they serviced it. I doubt anything they did caused the problem, but if it did the quicker you take it back the better.
A slipping torque converter clutch would cause similar symptoms, which could be caused by a bad solenoid, bad torque converter, cracked case (internal), etc. Now that's not the only thing that can cause that symptom but it's the first thing that comes to mind.
It's possible that there is a programming update for the car's computer that may address the TCC issue as well.
I wouldn't worry much about the wrong billing information being in the computer, that's just used for billing. The computer they use to check for updates connects directly to the car so that would be correct if they hooked it up, however on just an service they wouldn't normally do that. Depending on the dealer they may or may not check the vehicle for updates, service bulletins, and outstanding recalls. They use the VIN for that if they did and if the VIN was wrong on the repair order then they may have checked the wrong VIN when checking.
Again I would take it back to the dealer immediately to have them check it out.
Based on your comments this isn't related to the recent repair. There is a TSB (Technical Service Bulletin) that addresses your concern.
Condition Customer may report shudder or RPM fluctuation while at
cruising speed in 4th, 5th, or 6th gear. Technical Background
Torque convertor clutches may have excess slippage while cruising.
The solutions range from updating the TCM (Transmission Control Module), Fluid change, and replacing the torque converter.
This doesn't mean that that's what's wrong with your vehicle but it's the place to start looking since this is a known issue.