1985 K10 need new transmission

I've got an '85 K10, 4x4, 350 with a 4 speed transmission (SM465). What would it take to put a transmission with a 4th or even 5th gear? And what transmission would you reccomend?

I've even thought about going auto but not too sure how costly that would be.

Any help would be great.

Clutch adjustment, needs to be bled, bad pressure plate? How much play is there before you feel the pedal start to move the pressure plate?

//2000CAYukon