1999 Dodge Truck Won't shift from second to third

Trans ran perfectly. Then stopped shifting from second to third. Wouldn't change gears, even manually. I checked all connections into trans, checked trans fuse under hood. Then I pulled apart one conection at a time and tested. When I pulled off the connection that is on the drivers side of the transmission a little above the half line and set back a little. (There is another connection on the drivers side, it is lower and further forward then the one I am reffering to.) When I pulled this connection and drove the truck, I could shift just fine through all the gears but ONLY manually, when I am in third and really push the pedal down. No gear change, no kick-down.
i put the connection back together and the trans is back to stuck in second with no shifting even manually.
the trans never slipped or shifted really hard, there was no noises or anything out of the ordinary before this issue.
thanks in advance for any help