i just swapped out the original th400 in my 65' pickup with another th400 out of a 79 pickup. everything bolted up fine, but now i cant manually shift under load, i have to let off the gas to move the column shift lever. is there something internal that could be causing this? or is linkage the only possibility. its got me scratching my head causs the old tranny worked fine. the 79' th400 worked fine as well before being pulled.