Tvheadend

Hello - I'm having a strange problem with my setup where only 1 HD, over-the-air channel seems to have issues. All the other channels I've checked appear to be playing real-time without incident. I believe the issue is in my HTPC hardware or software (and not the TV or other hardware) because I have a separate, stand alone tuner that I can check against and its feed has no problems.

The symptom I observe is random stuttering and stopping during live TV on one channel. Sometimes playback resumes normally without missing program information but other times the video seems to be in fast-forward mode, almost playing at 2x or more to 'catch up' to the incoming feed. On rare occasions the feed will freeze completely and I have to reboot the Pi.

My hardware:
Raspberry Pi B+
Kworld UB435-Q, (DVB and ATSC USB tuner, of which I'm using the ATSC because I'm in N.A.)
Seagate Backup Plus USB 3.0 Portable hard drive plugged in to an external, powered USB hub.

Software:
openELEC 5.0.0 for Pi.
tvheadend, the version in the openELEC distro.
MPEG2 codec from the Foundation.

I've tried changing a number of settings on the Pi and in tvheadend to reduce the load on the Pi.
1) Audio feedthrough is enabled on Pi
2) All EPG capability is disabled in tvheadend (I read in some other forums that this could cause the freezing).

Any suggestions you have would be greatly appreciated. I'm so close to replacing my existing PVR...