need help with prop for 27ft warlock
 

ive got a 27ft warlock with a built 427 bravo xr upper with imco 1.50 gears, 2in lower unit which ive added a 1in spacer...was running a out board chopper 28pitch prop that did great....some told me i needed a bravo 1 28 pitch, so i bought it and now im blowing the prop out off the hole and have about 25% slip...im only running 4500rpm at 65mph..all this inboard stuff is new to me....any help on how to get rid of this slip coming out of the hole and geting my rpms up would be great....the motor was built to turn 6500 all day long but i cant get there....i tried a standard hieght imco lower with 1.35 gears and i couldnt even get up on plane but no slip...thanks for your help