1999 Ford Explorer new transmission locks engine

Transmission problem
1999 Ford Explorer 6 cyl Four Wheel Drive Automatic

Hello, my transmission lost drive on friday so as I had a spare box I thought I would change it. It was all going well untill I went to tighten the new transmission up to the engine. When I went to rotate the engine it was locked tight. But if I back the bolts off a few turns it frees off. The torque converter was full socket when the box was going in and it went straight on to the guides, and all four torque converter bolts are through the holes. Thanks for looking.