1984 Monte Carlo SS, L69 5L 305CID, 3-speed automatic:

Hello: I was noticing a bogging sensation between 40-50 mph while lightly feathering the gas pedal. I added 12 oz of Lucas fuel treatment/cleaner to about 3/4 tank of gas and drove it around. The bogging sensation seems to have disappeared. I thought, wow that is too easy. Gas tank got down to 1/4 tank, so I filled it up with 90 octane gas (with dreaded 10-15% ethanol..ugh) and did NOT add any Lucas fuel treatment. Low and behold, the bogging sensation is back. Do I need to add Lucas at every fill up now? Is it perhaps related to the ethanol in our modern-day gas? I don't have any ethanol-free gas stations around me so I don't have much choice. Any thoughts on this or anyone experiencing something similar? I was thinking it might me transmission-related, but when it went away with the gas treatment, I dropped that thought. Now the thought has re-entered my mind with the bogging having returned.