20Mustang01

Hey guys/gals
I just got this car knowing it had this issue. It won't go over 45 or shift past second gear. It has a CEL for three codes, one is p0340 which I replaced that sensor but do I have to replace the whole synchronizer? Second was p1285 and p1309. I think the last two were over temp sensed codes? And the guy at auto zone said the cam sensor is probably the one keeping the car from shifting so that's why I thought I could get away with just the sensor.
The car will shift normally from 1st-2nd, but in D it will eventually start to rev like its in neutral. If I put it in 2M it will drive as fast as I make it go.
Trans fluid is dark and it does kinda smell but not like the "burnt popcorn" smell. Just smells like oil. Really at a loss for answers, hope this is just sensor related!
Any help is appreciated, thanks!

2001 v6 3.8

Fink

shift solenoid.

i had this same issue just a couple weeks ago. you have to drop the trans oil pan to replace it.