Code P0700 - means that the engine control unit stored this code because the transmission control unit, caught some kind of a problem with your transmission. This code always pops yp on engine computer if transmission is faulty in any way.
Code P1776 - means that the pressure switch is stuck in neutral and low reverse. This is a part of the solenoid pack, which is serviced as an assembly.To replace this part you have to take an oil pan out, disconnect the shifter linkage, disconnect two connectors (one of them is located on the passenger side top of the transmission, the other on driver side, big square connectors). The valve body has to be removedand the solenoid pack must be replaced. At the same time as the valve body is removed , inspect the accumulator pistons and don't mix up the springs inside those pistons.
Note: One accumulator piston has a cover, you need to remove the snap ring in order to be able to access the piston.
Transmission oil must be checked with an engine running ant transmission in neutral. This is very important.
Hope it helps, but not sure if you are able to do it by yourself.
By replacing the valve body, it is only about 30% that it will fix the problem as this specific code shows problems with solenoid pack but not valve body (as I described before). Your car has a lot of km on it, and usually at 155000k which is almost 100,000miles(here) the whole transmission is recommended to be rebuilt, as after 100k miles it starts giving various problems and showing symptoms. So in your case I think it would be better and cheaper to rebuild the transmission in a long run in order to avoid further problems.
Hope I answered your question.