Why won't my transmission engage when put into any range?

I have just installed a engine that has around 69,000 Miles on it. The blazer was driving when I pulled it into the shop and since I got the new engine installed when I engage the transmission into gear it will not do anything at all. I made sure that the torque converter was engaged properly with the trans pump grooves before I re-installed the new engine. I got all the torque converter bolts lined up with the correct hole on the mounting plate (Flywheel). Installed all the trans to engine mounting bolts, got all connectors and sensors hooked up, no lines we pinched during installation, transmission has proper level of fluid. Can anyone tell me where I went wrong during the installation process? Or can anyone tell me what I need to check or do to try to fix this problem? Again the transmission was working before now because I drove the vehicle into the shop.