If I went back to a stock pulley size (from 3.4"), stock spark plugs (from Autolite 104's) and stock t-stat (from 180 t-stat) and I have a custom Overkill PCM tune done, would I need to get the PCM re-tuned? I believe that I still have my stock PCM as well if that would better suit me after switching the mods out.

Thanks!

You'd be better off to go to a stock PCM. The fans will come on and run constantly with going back to a stock t-stat as he changes when the fans come on/off on his tunes, as well as the timing advance and fuel tables will all be different.

Running the overkill would be fine, but might as well just put the stock back in. Or leave in the 180 tstat for the reason Randall mentioned.

I'm running a ZZP tune with stock Tstat and the rest. I like some of the other stuff it provides. My mileage has stayed the same and have had no ill effects that I can tell.

Maybe it was my perception but it seemed like the 180 t-stat and Autolite 104s hurt my gas mileage quite a bit. That is the main reason I am looking to change out the mods. Do you know approximately what the effect of those items are on gas mileage?

Iirc 104s are copper plugs. Those need changed out every 5 or six thousand miles because they were out.

180 tstat will hurt gas mileage, but I can't say how much. I would be surprised if it was more than 1 mpg. Plugs shouldn't really make a difference unless they fouled up from being too cold. My guess would be the 3.4 in combination with the tuned PCM are the biggest contributors to worse mpg.