Will I regret change to 3.55s from 2.76s

I think your mileage will suffer more like 3-4 miles per gal. That would be around 20-25%, from what you are getting now. If you do mostly city or around town, then you will on the right path, but if it is mostly highway speeds, I would leave it at is.
Lol as planning estate kind of thing with the only responsible kid.

4.11 or 4.30 for thrill and or die putting it off the Highway or County Road into the lake, river canyon for the grocery getter.

Faak it ! Working on the Trust, Will and making sure one of the kids understands 3 gun cabinets and contents. LMAO