About... 3 Days ago now, I got into my car and found that it would not go into 4th(OD). It has no issues driving in 1, 2, & 3, but it will not shift into 4. (Proper take-off, throttle response, shift points)

I've done a bit of reading, and have found out that it could be either the 4th clutch shaft, or the solenoid.

Are there any specific symptoms that I should look for before purchasing new parts? If so, what are they?

 

tear it apart and inspect the 4th clutch shaft and clutches then go from there.

 

that's exactly what I figured.