Hello, I have a 2007 Pacifica 4.0 limited. And I keep having the same issue over and over again. It will not come out of limp mode and will not shift out of first gear. I took it to get the computer replaced on it and it worked fine for a about a month then it went into limp mode again. Took it back to the transmission shop and they said I need a rebuild. When I picked it up it was out of limp mode again and drove fine again for about another month then it locked into limp mode again. I don't think it the transmission itself. And I can't seem to figure out what the cause is. I don't have any other issues with this vehicle beside the limp mode.

 

Getting the codes with an OBDII scanner is going to be your best place to start, as it will give you a place to begin focusing on.
I believe there are 80-ish transmission codes(P07xx).
My 07 Pacifica Base 4.0 recently went into limp mode and produced a P0755(shift solenoid B malfunction) code.
I replaced the solenoid pack and so far it has cured the issue.
If your transmission is freshly rebuilt, I would think the problem is something like a bad wire, a bad ground, or a sloppy connector pin/socket.
Again, the codes should lead you in the right direction.