I had the same problem with my 580sk, turns out there were 2 problems. Previous owner put 3/16" dia. clevis pins in the linkage where it connected to the transmission should be 5/16" creating a lot of slop. However the bigger problem was all the slop and wear in the shifter it's self, the base of the shifter should be a nice square shape to properly engage with the shift selector plates. I had to build it up with weld and machine it back to original specs. Also there are bushings that were worn out in the selector plates, bronze bushings $1.50 ea at the local bearing shop. Once reassembled with all the wear/slop removed it shifts great.