Could you give us an estimate of the lengths of tailpipe before and after these large diameter mufflers?

Your post made me think that surely
4 inch diameter pipes
have lower exhaust gas temperatures (EGT) than 2.5 or 3 inch diameter.

If the EGT changes then the RPM where annoying resonances occur changes.

Weather changes EGT, including humidity.
Makeup of gasoline changes EGT, especially percent of ethanol.

I now realize I have been “wearing blinders” as regards another important factor in EGT.

Changing to bigger pipes would move resonances.
Changing to smaller pipes would too.