07 caravan new transmission issues.?

I just put a new rebuilt transmission in my Mother inlaws Grand Caravan. I got the thing put in and slowly filled it with Transmission fluid working threw the gears reverse and forward gears intill a little over 9 quarts. anyway it shift into all gears sometimes but most the time it don't shift into all 4 just the first 2. I took it down the road one quick time and it jumped out of gear and only had reverse. so I cut the van off and cut it back on and forward gears was back but still only sifts threw all 4 every once in awhile. sense it shifts threw all gears obviously its not a internal problem, so it must be electrical sensor or something, I'm just trying to figure out what sensor or wire that would cause it to not shift like it should. any help would be great. Thankyou.