Thanks for all the info, I'll gather whatever info I can as I've had
different diagnoses, false fixes, and opinions from 5 techs now. All
of the return filters and vents I have replaced and seem ok. Here's
the latest:
-I spoke with the owner of the company that installed and has been
servicing the unit. He says one of his techs felt the TXV valve was
bad but they worked with Bryant over the phone who said the reversing
valve was bad based on the data given. He said it would be close to
$1000 to replace both and I should call Bryant and bitch to see what
they'd do since the unit is only 14 months old.
-I called a new hvac company for a 2nd opininon. They sent a tech
out. He measured the refrigerant psi for the lines attached to the
condenser. He noted the pressure was climbing from 200 to almost 400
psi, at which point the release valve kicked in and it would soon
start all over again. He had eventually gotten the pressure stable
and said he believed there was contamination in the line and the issue
was now fixed (although I found no change later on). This is the info
he gave me on what he did:

-found system overcharged
-found system heat pressure raising to 450psi from 210
-pumped system down, inspected piston at liquid line at condenser &
screen at condenser. Found a small chunk of possibly brazing rod
-flushed nitrogen through lineset to make sure there was good flow
-pulled system into deep vacuum
-recovered some of refrigerant to proper charge
-system working properly
-suction & liquid pressure steady
- 10 degree superheat LO 80
-12 degree subcooling Hi 200
-18 degree delta T - compressor amps 10.1

I called the company back and they sent out another guy. He energized/
de-energized the reversing valve using heat and cooling but it did not
help.
He had been looking at the air handler and says there's no filter
drier installed and now the system needs to be cleaned out, txv
replaced, filter drier installed and we mostly likely don't have a
filter drier on our other system (although that one's been functioning
ok).
I looked at the documentation for this unit and the filter drier is
listed under optional equipment but another page says it is suggested
in all field-connected split-system heat pumps. Can the absence of
this filter really cause the issue? If so, is this a major mis-step
of the installers to not put it in?