spun prop

I just purchased a new to me 1998 230 Overnighter with a 5.7 L 250 HP and Alpha One drive. The boat only has 250 hours on it and runs great. I had it checked out by a repuatable marine mechanic before I purchased it and had him install a new 3 blade aluminum prop 15x17 i think. I took the...

If anyone can offer some advice I would really appreciate it. I have a 23' 1995 sea ray sundancer with a 5.0 merc/ alpha one second gen outdrive. stainless rapture prop Problem: I have no thrust in higher rpm's and I am not able to get on plane Possible reasons: 1) I keep the boat in the bay in...