Suzuki 85hp outboard

PLEASE HELP.....

Boat operates different out of water than it does in water. When it is out of water both reverse and foward work properly. I can shift to both with ease. And throttle up and down and rpms rev up when supposed to.
However. When the boat is in the water (under load) reverse will just grind and not catch. But foward will catch easily. And when it does I can throttle all the way up and the rpms do not change from idle rpms. And boat does not go faster than an idle. So really trying to figure out why my rpms do not rise when throttle is open in water but will out of water.

Sounds like cables are not installed / adjusted properly.-----And running on the trailer is NOT a good indication of motor condition.-----Did this problem show up suddenly ?-----Tell more of the story !

Well I just got the boat about a month ago. And was running it at home to see if it was operating properly and when it seemed ok at home I thought it would be fine in water but then this happened. I have already ordered cables but was confused at why they would operate right out of water but not in water

For one thing if the clutch dog was just touching the reverse gear ( not properly engaged ) it would spin the prop on the trailer.-----No water around to cause drag / load on the prop.------Or the water pump was replaced and shift linkages are out of adjustment.------Model # and serial # are ?----Why did you rush out and order new cables ?

The cables were rotten and cracked anyway.so just a precaution. But the water pump had been messed with I know because there was an old one in the boat when I got it. But pees correct so I assumed it had been replaced. Just didn't know in that part of the motor had something to do with linkage adjustment . Also I dont know model and serial number off hand