Prop recommendation

[geezer1]

OK Jay, here goes...1996 Force, 90 HP equipped with a Michigan Wheel alum prop (#31043 = 13" dia., 19" pitch) on a 16' 1996 Skeeter SS 90 SP. Boat dry wt is 800 lbs. With outbd motor, troll motor, 3 batteries, 18 gal fuel, & 2 fat guys with equipment, we're looking at around 1900 lbs. Motor particulars are: Mercury 4.25" gear case, thru hub exhaust, 15 tooth spline, 2.30:1 gear ratio, recom max RPM = 5250. With motor mounted to transom, fully loaded, at WOT & trimmed full up, RPM was 5250 with GPS speed of 42 mph. Installed CMC PT-130 to replace faulty trim unit. I'm sure you're familiar with this unit. With the 5.5" of setback I now have, I raised the anti vent plate to 2.125" above the keel. I ran the boat with no passenger & 1/2 tank fuel in test #1 with the following results: Trim full down, WOT = 4650 RPM, GPS spd @ 31.2 MPH. Trim up (just before porpoising), WOT = 4850, GPS spd @ 33.7 MPH. Raised the motor another 1.5" (anti vent plate now 3.625" above the keel) for test #2. For this test, I added a passenger (160 lbs) & had the following results: Trim full down WOT = 4650 RPM, GPS spd @ 31.2 MPH. Trim up (just before cavitation (?) there was no porpoising here)WOT = 5000 RPM, GPS spd @ 34 MPH. In all of these tests, 16 lbs of water press was maintained. Water was calm with little to no wind. In all cases, the boat was slower to plane out than when the motor was mounted on the transom. Jay, would the 5.5" setback change things up enough to need a 17 pitch prop, where a 19 pitch worked fine with the motor on the transom? Your thoughts on all this, please.