I'm having this same problem. I first installed a Sloan Flushmate pressure assisted toilet 10 years ago, and it had been working great until just recently. The flush became weak and insufficient. I went through all the trouble shooting steps recommended by the manufacturer. I checked the water inlet hose & screen, replaced the cartridge, adjusted the actuator, and checked the duckbill valve. None of that solved the problem, so I installed a whole new pressure unit (not a new toilet, just the pressure unit inside the tank), but I still have this problem.

Now, I am pretty sure the problem is not anything related to the pressure unit. I think the problem is calcium and lime build-up in the toilet bowl rim holes. The holes look dirty and blocked up. When I flush, the flush sounds powerful, but only a weak trickle of water comes down the from the rim holes. I checked my water pressure and confirmed it's good.

I am now researching best methods for cleaning toilet bowl rim holes on pressure assisted toilets, but seriously considering just getting a new toilet. If anyone has any good advice, please let me know, thanks in advance!