First - test the secondary vacuum throttle shaft actuator (the prime suspect in midrange to top end power loss). Check all the top cover screws and the main mounting bolts to see if they're tight enough. Give the outside of the throttle plate a squirt of WD40 etc while it's running and see if there is a change in how it runs. If it improves for a second then you have a leak somewhere. If not then try this - with the air filter off and engine running get a buddy to keep the throttle open, cup your hand over the throats to try and starve it of air (not completely to stall it but enough to choke it), This might be enough to purge any debris in the jets and improve how it runs. Good luck!