330 planter people, I have a problem

I am assuming you have a common drive planter?  If I were to take a wild guess it sounds like the catch hook (not official terminology) is not fully clearing the teeth in the outer rim of the clutch.  This catch hook is a plate with a piece of rod welded perpendicular on the end, which sets parallel to the central axis through the clutch, at the outer circumference of the drive clutch and sits to the front/top of the drive clutch.  When the planter is lowered the rod is supposed to move away from the clutch disengaging the rim with teeth allowing it to turn and start the drive shaft turning.  When the planter is raised the rod is lowered to the clutch, catches a tooth on the rim which stops the drive shaft.  Next time you notice the shat is not turning look to see if the rod is currently engaged in a tooth.  I would try and refer you to a good manual picture but, although the rod is shown, it is not clearly labeled nor is an adjusting procedure given.  You can kind of see it on figure 171 page 140, in my manual anyway.

OK, the transmission clutch wasn't the problem. I got my Dad to drive the tractor while I sat on the planter. Turns out it was the two clutches down near the drive wheels. Guess what? They were on backwards. This was the 3rd season planting about 40 acres of soybeans. Doesn't take much to turn that shaft I guess. And of course it was all my fault. When i got the planter it was set up for wide rows so I changed it to narrow and I must have fliped the clutches around (although I can't remember ever touching those clutches). I did notice last year it looked like it was skipping a foot or so every once in a great while on all rows in the last 10 rounds or so. I forgot all about that by this spring though. Worked great after I flipped the clutches.