Time to rebuild?

When I first did the compression test, I used a borrowed tester that leaks down as soon as you stop cranking the engine. Today I bought my own tester that holds the pressure. Results:
#1 135 psi
#2 135
#3 140
#4 140
#5 140
#6 140

Possibly unrelated question: why can't I turn the engine by hand? My plan was: with the spark plugs out, make sure I can turn the engine by hand before reinstalling the plugs to do Bill's suggested "turn by hand and listen for leak down" test. Well, I can't turn it by hand. If I go to the driver's side and pull on the fan belt with both hands, I can move it a few degrees but it takes my full strength. I'm no he-man, but I'm not especially weak either. Thoughts? EDIT: Never mind--if I stand on the passenger side and pull on the belt while pushing on the fan I can turn it pretty easily.