Same problem on both my 83 Dodge van (318/904) and my brother's 83 Dodge van (225/904). My 904 is the 1983 original lockup version, my brother's 904 is a 1973 non-lockup unit out of a Dart (there's the A-body link).
Symptoms:
Slow engagement into 1st, random flare up at 1-2 shift...