Update. I tried ServoTimer2.h, and it was a disaster. Tremendous conflicts between the the servo and software serial. The sensor was reporting communication errors left and right, and the servo either didn't move at all or jumped with huge jerky movements. I haven't given up on that, but moved back to the regular servo call for more testing.
Another thing I tried was using a variable power supply for the servo. I was driving it with my Ruggeduino, with a voltage drop that didn't hurt anything, but not pleasant. Then I switched to a good 5V switched supply with connected grounds. That actually made things worse for the servo, but was needed for the Arduino anyway.
So, with the variable supply, the servo was much smoother at 4.5V. Still had problems, but not so bad. When connected to the Arduino 5V supply, voltage dropped to 4.8V, which made me wonder about voltage going into the motor. 4.8V not so bad, 5.3V (from power supply) worse, so what voltage is this thing happy at? Below 4.0, it didn't do anything at all. Above 4.5, the jerkiness in the servo increased.
I bought two of these servo motors. When I get the chance, I'm going to try the other one, to see if there's some difference. I suppose while I'm at it, I should try the servo driven by one Arduino, and the sensor connected to another, to better isolate the problems.
Ken