My old 24' Sonic twin O/B did the same thing w/my 3 blades. Would go 7 MPH on one motor and no faster w/o spinning the prop. Current 24' Sonic would plane on one w/a 4 blade Bravo but I sold those props and am back to the 3 blades.
I normally run 26's and always said I was going to buy a pair of beater 19's to throw in the boat for long trips.

I have towed and been towed on plane in the smaller 18' - 20' boats to get back in when a ways out.

If I didn't have 5 blades I don't think my boat would ever get up on one engine

It will help to pull the prop off the down motor as well as trimming it up. I've done it with 4 blades.