The car will roll marginally better, but 2 PSI is too small to see a measurable difference. EG see:
http://ecomodder.com/forum/showthrea...tml#post265379
Question about your big rims: has your overall outside tire diameter changed from stock? If so, how much and are you correcting your fuel consumption calculations to account for it? If your outside diameter increased, your odometer will be under-reporting distance, making your MPG calculations appear worse than they really are.