Stays in third gear

I just replaced the ECM with a rebuilt from Florida. They flashed and programmed it for my truck with the VIN and mileage. I installed it and my truck fired right up and everything worked, until I drove it and it will not come out of third gear. It starts in third gear and stays there. The truck would not start before replacing the ECM but the transmission worked fine before when it was working. I do believe the new ECM is not sending the correct signal to the transmission for it to shift. Would this be correct since it worked before the other ECM went? It shifts from first, second to third if I do it manually but once in drive will not go to fourth or shift down.