The starboard drive will not trim up when in gear in the water.It will trim up and down when on the trailer and out of gear in the water.When you start moving it doesnt trim up,the motor is working fine with new oil?

What kind of shifters do you have?

The drive won't trim up when on plane? of just idling?

When its on plane and idling put it back on the trailer it moves up down.

Has the trim hoses, from the trim pump to the trim cylinder ever been removed by yourself or maybe a previous owner?

I had the same issue when I got my boat. The trim worked on the trailer and at the dock, but once I put it in gear the drive would not trim up. For me it was a simple fix, just swapped place on the trim lines on the pump.

bl

That's where I was headed. The trim pump has a low pressure and high pressure side. The high pressure side is for lifting the drive up.

Yes the the trim cylinder was replaced.

I would check your lines to make sure they didn't get put on backwards.

if the lines are correct, was it a new cylinder or a used one?
if used the check valves inside the cylinder could be bad, and not able to hold the pressure of the sys. when put into gear.