1995 60hp kickes out of reverse

[ColdwaterLake3]

1995 60hp Mercury bigfoot on 20ft Pontoon. 3 weeks ago I was backing away from the beach when I hit a concrete block (someones old mooring block) it broke my prop. I replaced the prop now I am having trouble getting into reverse or staying there when it gets into reverse. With the motor tilted up and the prop out of the water it seems to work fine shifts fwd and rev. but with the prop in the watter when I shift into rev it mostly just clicks if it does go into Rev. it will kick out if I give it any gas. I am trying to find the proper manual for this motor now but any ideas that will get me back on the water would be nice.