1992 ford conversion van shifting hard

Gjac wrote:
I had a 1992 Ford conversion van with a 351 eng and 4 speed transmission that I had rebuilt at 160,000 miles before giving it to my son. It now has 189,000 on it and is shifting hard when driving normally in D. It seems to hunt for a gear then bangs into gear. If it is shifted manually from 1 to 2 to 3 it shifts better or if it is floored in D it will shift better. Does any one have any ideas what would cause this? Plugs, wires, cap and rotor were recently changed.