If the selector is OK then the park linkage should prevent movement. Why did you add ATF as if there was enough to drive forward there should be enough to go back. Too much ATF will cause foaming and poor shifting etc. Disconnect the cable at the gearbox to see if you have all the positions and it gets park. What positions can it be started? Has any one had the valve block out and misaligned the manual valve? Again what year 4/5 speed? Does it bind in reverse ie not like neutral? Does it drive forward in N ?Forward clutch slipped and then welded up.
mags
February 2010