5 unique Check Engine Codes (12 codes, total) --- Transmission not getting above 3rd / 4th gear

I have a 2009 Chevy Avalanche LT-2 (4WD), purchased in 2012.  The check engine light
came on, had it scanned and they told me it was a loose / faulty gas cap.  So, I
changed the gas cap, light went out and then recently came back on.  When I had it
scanned today, the light was on, but the truck appeared to work fine (mechanic may
say otherwise, but from a layman's perspective, it operated as I would expect it to).

The scan came back with 12 total codes, 5 of them being unique: U0100, P0449,
P0700, U0073 and P0445.  What appeared strange, to me at least, when I got out onto
the highway, after the engine light scan, the truck could get up to 3rd or 4th gear and
then just stayed there, not shifting into 5th or 6th.  Flashers went on and couldn't get
much beyond 45 - 50...not a fun speed on an at-speed 495 (DC Metro Area's 8+ lane
"Beltway").

According to the Zorac OBD Check Engine Code Android App (not trying to advertise
for them, just that it seemed to work well for me in trying to find code information):
1. Chevrolet P0445
Evap Emission Ctrl Sys Purge Ctrl Valve CircShorted

2. Chevrolet U0100
Lost Comm With ECM / PCM A

3. Chevrolet P0449
Evap Emission Ctrl Sys Vent Valve / Solenoid CircError

4. Chevrolet U0073
Control Module Communication Bus Off

5. Chevrolet P0700
Transmission Control Module (TCM) Requested MIL Illumination

Aside from, "Take it to your mechanic, yesterday!" any recommendations?  I know that
disconnecting the battery won't fix the issue, but would that clear the codes long
enough to safely get the truck to the shop?  There are enough back-roads that I could
avoid the highways on the way home, would have this morning had the transmission
acted up before I hit the highway (not trying to drive dangerously nor ignorantly).

Many thanks in advance!!