Wow, quite a few replies. Sorry it took so long, had a long day at work.
Anyway, I was able to borrow a crappy o-scope from work, but was able to make some more measurements and I know what my problem is now.
The frequency is right about 50Hz. By looking at the o-scope, it's actually around 52Hz, but that could be a calibration issue, the fault of a tiy display, or maybe that's what it is supposed to be. The frequency is constant whether channel 3 is in position A or B - just the duty cycle changes. Peak voltage is right around 4.8v.
When channel 3 of the receiver is at position A, the duty cycle is 4%. When it is at position B, the duty cycle is 2%. Not much of a difference there to work with! Those servos must be pretty precise indeed!
I checked these values on the throttle channel (2) and the steering channel (1) and they are the same, except I have a tad bit more range in duty cycle, but not much (maybe an extra 2% over the full ranges).
So, my question now becomes: how do I turn a 2% change in duty cycle to a 0v or 6v output? The comparator in my original design would have to be VERY precisely set! If this cannot be accomplished using analog circuits, I'm open to other methods. However, the whole circuit must be kept very small. To complicate this futher, this circuit will be in an R/C truck along with servos running and a high amperage PWM drive motor controller driving a 3 phase brushless motor drawing upwards of 60-70 amps @ 14vdc (yes, you read right; 60-70 full amps), so noise can be an issue.