Two weeks ago our 4.3l OMC would not shift into forward or reverse. I replaced the entire shift cable to find the black knob at the control arm was busted. Once I replaced it, it worked fine for two outings, until the third outing it started not shifting. When sitting in the driveway there is no tension when trying to shift into forward, but extremely tight when trying to go in reverse. I took the handle off and the knob is intact. One mechanic thinks it could be the lower cable, might not be in sync, or could be the clutch dog in the lower unit. Any suggestions would be appreciated