Random Step Forward/skip/fast forward delays win7 VLC .wtv files

Win7 Ultimate
WMC
VLC
K-Lite Codec Pack
I've been using Media Center to record/time-shift 4 TV channels.
I play them back with VLC because it allows me to increase
the playback speed to 2X.
It's been working flawlessly for several years.

Recently, Avira AV went rogue and resisted all attempts
to uninstall it. I gave up and reinstalled the OS.

Now, I have a random symptom that I can't track down.
Playing the .wtv files with VLC.
If I try to skip forward, the first skip always works.
Subsequent skips may or may not have a 10 second or
more delay. The screen is frozen and nothing happens until
the delay expires. It's similar to a buffering problem, but the CPU
activity stays low and there's no obvious increased disk
activity.
This is file related. If the .wtv has the skip delay, it always
has the skip delay. If it skips correctly, it always skips correctly.
I initially suspected a codec issue, but that shouldn't be random.
Other recordings from that session may or may not have the
symptom. The symptom is unrelated to the selected
playback speed as long as I keep it below where the hardware
can't keep up.
There's a VLC setting "fast skip" that was not enabled.
I enabled it and the problem went away...until sometime
later when it started happening again.

..wtv files recorded before the system reload have never exhibited
the symptom.
Recorded files that exhibit the symptom continue to exhibit
the system when played at a later date. All files always play/skip
without delay when played with WMC.
I've copied the files to a different partition and the problem persists,
although it's somewhat random.
Rebooting doesn't help.
Defragmenting doesn't help.
Registry cleaners and unnecessary file deleters don't help.

The files play fine and skip fine using Media Center for playback,
but I haven't found a way to increase the playback speed with WMC.
That functionality is essential.

It sounds like it's mostly related to recording, so...
I picked a TV channel and restricted recording to one tuner.
Playback skip works fine.
I cycled thru all 4 tuners and all worked fine.
Since it's random, I still can't be sure that it's not a tuner driver or
configuration issue.

I copied a bad file to a different computer and it plays/skips
correctly in VLC. Same file played across the network with VLC
doesn't seem to have the problem, but the network speed limitations
to introduce a lesser delay in the skips.

If there were a way to increase the playback speed of WMC,
that would solve my problem. That's the only reason I
use VLC for playback.

I've reloaded WMC. I've reinstalled VLC. Nothing helps.
I've not found any log issues showing an error, but maybe
I'm not looking in the right place.

Any suggestions on what I might try to diagnose this random
symptom?