What are these transmission codes and how do I make the repairs?

I have a 2003 Dodge Intrepid 6 cylinder 2.7 ltr. - from reading the internet - this transmission problem seems like a fairly common problem with this car. Lots of complaints online, but NO resolutions. (Not that I've found)

History:

When slowing into a lower speed the transmission "limps in" (goes into a lower gear) the RPM's will rev up past 5 (x1000) if I attempt to go any faster than 45mph. A quick fix is to pull over, turn the car completely off and then restart the car then I'm good until it "limps-in" again the next time I have to slow.

Also, when the vehicle is "cold" and I put it into a gear (either forward or reverse) it revs up like it has to "catch", then jerks into gear and goes.

I took the car to an auto shop and they put it on their computer and it came up with the following codes:

PO841 - Low and Reverse clutch Pressure Switch Circuit
PO871 - Overdrive Hydraulic Pressure Switch Circuit
P1776 - Solenoid Switch Valve (left rear piston)

the mechanic at this shop said that they don't do these repairs but gave me some information on a place that does.

Before taking it in I have a few questions:

What kind of repairs am I looking at?

Are these sensors?

Or Is this something that will need to be done in a "re-build'?

Is this something that I can do on my own? (I am fairly capable when it comes to replacing or exchanging minor parts like belts, hoses, brake pads, rotors, radiator, alternator, starter - etc....)

Thanking everyone in advance!