2001 Ford Ranger Seized engine

I have a ford ranger 2001 with a 3.0 ltr engine while driving truck it blew a spark plug from cylinder so figure e is garbage. I bought and installed same engine it started but when put into gear lost all power, and backfired as I tried to accelerate brought engine back to where it was bought they said a cylinder had no compression. Bought another engine, out of same exact truck, I heard it run and was strong engine! I then installed engine (again!) Started truck ran good, put it into gear and the same thing it lost all power and backfired then made a loud screech and died. Took plugs out and cannot turn crank like engine is seized. Thinking that maybe my problem is the transmission? Maybe torque converter wasn't in gauged completely? But cannot turn crank in order to remove torque converter nuts. Hopefully someone can help me?