Hello and Thanks in advance!

Hello to the forum and thanks to the knowledgable people here. I have a Husqvarna zero turn with a Kawasaki 24 horse v twin, model FR730-BS13-R. It lopes. It's better under a load. It is also usually better with a slight to medium amount of choke applied. It gets worse or better at intervals which I haven't figured any pattern to. So far I have-
 

• Taken the bowl off the carb a couple time, attacked with carb cleaner
• New air cleaner
• new fuel filter
• emptied and cleaned the gas tank
• changed the plugs

No love. Suggestions?