Just replaced tilt/trim pump.....something not right

[GSB Cruiser]

The trim/tilt pump for my volvo 290 was leaking so I went to a boat yard and found an exact replacement. I installed it and filled it with fluid and it works, but while i'm trimming the outdrive up, it will suddenly stop lifting it up and the tilt motor will change to a more high pitch whine. If i let off the switch and try it again, it will work again. I managed to raise it all the way up, but it took an even longer time than usual. I checked for more leaks and did not find any. I noticed it took a really long time to put the outdrive down as well. It is the old style Prestolite pump with the filler on the side. I thought maybe it needed more fluid, so after i lowered it i tried putting more in, but it wouldn't take it. Thanks for any help guys.
OUTDRIVES........UGGGHHH!