Short in the wiring or a break in the wire. Could also be a poor ground
to the engine/trans. Also check the connector itself, just a little crud
will cause problems.

It is likely the problem that caused the original problem. FYI NEVER
assume that ANY error code actually shows a bad part.

Just because a sensor is new doesn't mean a sensor is good.  They sell
an awful lot of cheap crap out there these days.  If it isn't the
sensor itself wiring would be my next best guess.  Could be as simple
as corrosion in the connector for the sensor.

              Steve B.

The good thing is that you have solid and repeatable symptoms.  From a
quick glance at your wiring (I chose 2.5 liter engine, might make a
difference if I guessed wrong), the PCM and HEC (instrument computer)
both receive the same paralleled VSS signal wire input.  There may be
more computers that use a branch off of this circuit, but it would
take a complete system diagram (don't have one) or a lot of time
(don't have that either) to see every device served by this signal
wire.

My point here is that you can tell from the schematic, the assumption
that two different VSSs couldn't cause the same problem, and the
symptoms that you are either:

1) losing B+ at the VSS

2) losing ground at the VSS

3) losing signal continuity at the VSS

4) shorting the signal wire, most likely inside a companion computer

The first three of these possibilities could be tested with a
multichannel scope and a test drive.  You know that the best test
point is right at the VSS harness, so start there.  If a B+ or ground
abnormality coincides with speedo dropout/trans downshifting, then
bingo.  If the signal wire drops to ground during the failure event,
then it is either opening somewhere or being shorted to ground (you
must be moving to see a fluctuating square wave pattern on the signal
wire).  Then procede to some sort of powered or ohmmeter wiggle test
method of the signal wire in the shop.  If the electrical open doesn't
reoccur using the wiggle method, I would suggest that one of the
computers is grounding the signal wire intermittently.  Take note
whether the problem occurs mostly over bumps, what speeds, wet out or
dry, anything that might help narrow down a plausible cause for this
intermittent behavior.

Sometimes a set of symptoms in a specific car/engine combination are
the result of a high failure rate of one component; IOW if you ask the
right guy, he'll know right away where to start looking to save time.
This may be the case but I have not heard of anything specific to your
vehicle.

Toyota MDT in MO