Prop Question

[TomNJ]

I have a 1980 Cruisers 23' cuddy with a GM 305 and an alpha drive. I am having a hard time getting it to trim out at slower speeds. I mainly use this boat for fishing so speed is not a major factor for me and would like to keep the bow low. It also doesn't trim out until about 4000 rpm's and then I can back it down but I lose it at about 3200 rpm's. Is this a prop issue?

Thanks