It could be the added detergents in the Lucas fuel treatment. Over the last few years the EPA as reduced the required amount of detergents in gasoline by 50%. I noticed last year one of our cars was not getting the MPG it did previously. It also didn't idle as smoothly. After adding a bottle of fuel injector cleaner and running that tank of gas through, the average MPG started climbing up. The idle also smoothed out. Now I it's hard to tell if the engine is even running.
There are 'Top Tier' fuels that have at least double the EPA required amount of detergent. If you use gasbuddy to check fuel prices you see the stations that are rated 'Top Tier'. Mobile, BP, Costco and Shell are some Top Tier fuels.
I don't know if it's necessary to add detergent to each tank but depending on the type of fuel you use it wouldn't hurt to through some in every now and then.