1994 O/D won't stay engaged

Just replaced the engine in my 1994 Villager and now the O/D won't stay engaged. When you turn off the O/D it runs smoothly. We are planning a 6 hr trip in a week and don't want to run it that long without O/D. All help is appreciated.

I’m not sure about a 1994 Mercury, but I had the same problem with a Buick once after I replaced the tranny. There was a connector that I missed, it was for the electronic lock-up for the torque converter and was necessary for it to stay in O/D. Once I reconnected it, it worked fine. Hope this helps.

Thanks for the advice. Rechecked all connections and still not working. Reset the timing and it helped some but still won't stay engaged for longer than 10-15 seconds. As long as you are accelerating it stays engaged but when you hold the speed or slow down it kicks off. When we changed the CV joints there was a lot of trans fluid that leaked out but the dipstick still reads full. I added more just in case but still no change.