What are your motor heights and water pressure???

According to my calculations with 10 percent slip which is a little high at 8000rpm and 32" pitch props you should be running 117mph. Are you saying you can spin 32" props but not 30" Props?
Turning 30's will only make you turn higher RPM's and possible go slower.
Raising the motors will increase speed and rpm but i would first try and figure out why you have a 19% Slip with the motors only an 1" above the bottom. Are they on set backs? If so how far back?
I would guess the props are not 32's but maybe a true 30. Could have been reworked.

Hopefully this covers most of what you guys have asked: motors are mounted on 5" jackplates, water pressure is well above 10psi, and the props have been re-worked. They're supposed to be 32s but it looks like they might not be(?). The 30s never worked out. Not sure why the numbers are so bad but the boat has seen 106mph with those props. Any ideas??

106 w/ros ecms is god awful. Where are u you located?

I do know that when I ran un labbed props I lost 5 to 10 mph. The rpm's were up but so was the slippeage.

Yes. Have only ran Merc lab props.

Stock 280 ECU's redline at 7750rpms.

Sounds like you may have a set of 2:1 gearcases. If you drop the cases, the top of the sportmaster should be stamped with the ratio. 1.75, 1.87 or 2:1... 32's and 8k at 106 works out to about 12% ish...