225/40-18's in front?
255/35-19's in rear?

I know that there are dispersion in tire sizes from one brand to others regardless of what is stated on the tire, but not enough to create a problem IMO. The only people that have had problems were on cars with lowered suspension. Other have installed oversized tires with no problems. You don't say whether its front or rear? L or R or both sides? Have you tried taking back to where you purchased your tires?
Let us know the outcome.