Auto's w/31's had 4.87 oem gears, so you wont be over geared w/the the 225's. However your mpg will suffer w/31's. My sister got only 13 combined w/her '95 3.0 runner w/31's and 4.56 gears. Since you only have a 2wd and want to run 31's, it will only cost you about $2-300 to get a used 4.87 rear oem diff.

How bad your mpg loss will be w/31's depends on what it s now. Than figure what 11% less will cost you, since 31's are 10.71% taller than the 225's, you will basically go only 89 miles on the same amount of gas that you used to go 100 miles.

Depending on your current mpg and how far you commute, the extra $300 for the 4.87 diff may not be that much w/the current cost of gas.