Worse gas mileage after tune up

2001 V6 4.3 with body lift and oversize tires. 198,000. Ive always got around 16 mpg up to 192,000, then it dropped to 14 mpg.
One day it wouldn't start, turned over but wouldn't start. Moisture was getting in the cap and rotor during extreme fog conditions.( I've changed these several times over the last year, and still not 100 pct sure I've fixed that problem. Won't know till the next fog). Anyhow, when it wouldn't start I also changed plug wires, PCV valve, and replaced the plugs with iridium. I also replaced the fuel filter and air filter. The old plugs were horrible, so I expected my mileage to return to 16 mpg, or at least remain at 14, but instead it dropped to 12mpg.
(As a side note, my mileage dropped to 14 mpg when I got new tires installed, may be a coincidence, not sure). My tester reads no codes.
I have two questions, is it possible that installing iridium has actually made my gas mileage worse? Also, is it possible that IF my actual distributor is bad, it could be making the mileage worse? (If I get moisture in my rotor and cap again, my next step is to replace the actual distributor).
* Heads up, Im not a mechanic, I'm a 61 year old little lady who doesn't have the money to pay a mechanic to do this, so I'm learning about and doing lot more than I ever thought I would, or care to. I can now take the dog house off in 10 minutes, and put it all back in 30. I never wanted to get skilled at that. So with that in mind, please don't get too technical with your explanations, I'm not an idiot, but I'm not a mechanic either. 😁 Many thanks for your input.