toyota lucida gearbox fault wont engage 3rd replaced gearbox same fault ???

HELP!! I have just fitted another gearbox to my toyota lucida as the original didnt engage 3rd gear properly or O/D it seemed to be flickering about at around the 40-50km/h mark, I am pressuming it is electrical as the new gearbox fitted was fine in the previous vehichle.
I hope there is someone who has some input as we due to go away for a couple of days soon.
Thanks in advance. Jim.