extremely soft 2nd to 3rd shift

Well, I dont understand how my cable could be that messed up, I have my cable set at the exact same spot i have always had it set at, i can tell by looking at the cable at the carburetor.
The 1-2 shift is fine but the 2-3 shift is soft, and i dont understand why, It more then likely could be the shift cable, but if it is the shift cable i'm thinking it has some slack in it somewhere that i cant see. I had my friend get in the truck and floor the gas pedal and i checked the travel of the cable down on the transmission and with the gas pedal floored there was still room for the lever the shift cable hooks up to on the transmission to travel. (It wasnt pegged all the way) Could this be the issue?
Also i noticed that sometimes the shift is really soft and other times it's not and shifts fine. And while in 3rd gear when i apply throttle the transmission pulls well and does not slip at all. So I'm thinking this may be a valve body issue or shift cable issue because if it was a clutch issue it would most likely be slipping, right?