Rebuilt lower unit, wont sit in foreward gear correctly.

[Shwinkyyy]

Good morning,
I have a 1984 mercury blackmax 150hp. I did a rebuild on lower unit and yesterday after putting in gear oil. I noticed when in foreward gear prop doesnt spin much unless i really throttle her up, and i can grab it while in gear and turn it counterclockwise. I get no ratcheting or any kind of resistance. In revwrse gear i cannot spin by hand in either direction.
Also so you know i did not "shim" the driveshaft when i installed it. Could this be my problem? Or could it be gear shift cables?

 

[Shwinkyyy]

So just came back in from checking the shaft, it actually seems fine, gave it some gas and tried to hold the prop shaft, and its spinning good. I guess it doesnt spin much while idling?