To answer your question -- yes, there are individual solenoids in the valve body. This will identify which ones are which:
Sonnax Toyota/Lexus A750E/F Solenoid Identification
and this tells you a lot more about that info:
http://www.gearsmagazine.com/resourc...2010_4_all.pdf
Give these a read and share your thoughts. I might be inclined to dig in there and replace the solenoids before shelling out for a new trans -- especially if it passes the abovementioned Scotty Kilmer Shift Test which seems reasonable enough to be true in this particular case -- if you can make it shift into each gear, that means the gears all work, but the electronics don't know how to make it happen correctly which is where the solenoids and such come in.
I have done similar work (removing the valve body and replacing failed solenoids) on a Grand Cherokee. It's not difficult work -- just nuts and bolts -- but it is really messy and you'll want to be meticulous about keeping parts clean.