GPS partially working but inaccurate

[buster1015]

Background
I have a 2001 X5 4.4l and last week completed an oil change and reset the service indicator. Because I have an early 2001 it could not be reset using the dash buttons. Instead I used a jumper to reset at the 'Pacman' port under the hood. Everything functioned fine for two days. Then I drove on a rough dirt road that was quite bumpy. But, everything was still working after returning to paved roads including multiple uses of the Nav System and ignition on/off cycles. Next day the issues began.

Current Symptoms
I enter a destination address and map it. But, the direction arrow is not stable and spins slowly. My vehicle location displayed is very close to correct but sometimes shows on a nearby street. While driving my vehicle location will jump to a nearby street or show in the wrong direction. I have also noticed that when I turn on the vehicle the nav/radio screen takes longer to turn on than I remember. Seems like a good 30 seconds until it is on although the radio begins playing (if it was on before). This slow to turn on screen began the same day as the GPS issue. All other functions I've used are working.

Tests so Far
First thing I could think of to check was to go into the Nav Service Mode.
I looked at the Sensor Check menu which showed:
Wheel sensor: 0 when parked and increased proportional to driving speed
GPS satelite: 08 when parked and varied from 06 to 08 while driving
GPS status: Positioning known (at all times)
Gyro: always pointed in direction of vehicle travel
Direction: forward or backward and matched vehicle travel

GPS Tracking Info:
shows a list of 8 channels representing satelites
S/N varied but 5 channel's S/N were between 5 and 12
remaing 3 channels' S/N was 3 or 4

Thoughts
I don't want to just start replacing parts. Seems like some of the S/N values are a bit low. I'm thinking of checking the antenna cable or trying to temporarily swap in a know good antenna if I can find someone who has one. After that I have no idea what to do next. Any advice is appreciated.