While I’m driving between 45 and 55 mph my car will hesitate or jerk until I can maintain a regular speed. This happens when I’m driving local roads behind someone going slower… She loves high speeds and this does not occur.
I think the car may be just changing gears a little rough at these speeds according to the terrain. A sudden upshift to a higher gear while you are trying to accelerate on flat or downhill roads will feel like a loss of power (which it is, but it’s not a problem), and a downshift while travelling uphill will feel jerky.
If your check engine light is not on, I think you just have a somewhat jerky transmission/ gear ratio for the speeds you mention, which also translates into a nice and freewheeling top end. In which case, you’re right, your car is built to go fast on the highway, not follow slowpokes on local roads.
But if the CEL is lit, I’m wrong and you have a misfire and need to get the car diagnosed.
Try locking your vehicle out of overdrive and see what happens. It may be hunting for the top gear or it may be the lockup on the torque converter.
In earlier days (you don’t say what year your car is)we searched for a very long time on a 1985 533i BMW. It turned out that the still primitive fuel injection was going slightly rich then lean,causing this annoying (but very slight) surge.
Tell me the year and I look for TSb’s (and engine size)at times manufactures will put out "fixes’ for drivability issues.