I have a 22 year old Trek 5500 with the original Dura Ace groupset. To make the shifting more knee friendly, I decided to get a 11-34T cogwheel. The old Dura Ace 9-speed rear derailleur won't handle the chain wrap so I did some research and found that current 9-speed derailleurs should be compatible with the Dura Ace 7700 shifters. I ended up having a Shimano Acera rear derailleur installed. However, with the Acera rear derailleur the cable pull ratio appears to be out of whack by a little and I am having problems with the two smallest sprockets. Will using a M592 or an old Deore XT derailleur fix that?
All Shimano 9 speed shifter components should have the same pull ratio, so you should be able to use a Deore XT derailleur. But the Shimano Acera 9 speed (or even 8 speed) derailleur should work as well. 10 speed road derailleurs also have the same pull ratio, except for Tiagra 4700 and GRX groupsets.
It’s strange that you have problems with the two smallest sprockets. Does it shift to the smallest sprockets when you completely detach the cable? Then it’s a cable issue. If it doesn’t shift to the smallest sprockets even with the cable detached you’ll probably have to unscrew the lower limit screw by quite a lot. If that doesn’t help I’d suspect a bent derailleur hanger or bent derailleur.