Fuel additives and EGR cleaning/kits, what does Oppo think?

I’ve noticed I’ve lost a few MPGs a fill up recently. Granted this could be a number of factors such as driving style, location (recently moved), different pumps (fills the tank up to a different level throwing off the calculations.) etc

I’ve covered the basic mechanical stuff. The air filter’s alright. I checked the spark plugs a few months ago (I’ll check them again anyway) and they were fine. I guess I’ll go ahead and replace the fuel filter. Although I’m sure that’s not the problem, longer reasoning than is appropriate in this post.

Also what does oppo think of EGR valve cleaners/cleaning? I haven’t gotten any codes, but it’s OBD 1. I had an audible vacuum leak one time that didn’t throw a code. Seen some kits for anything about those specifically?

Anyway thanks!