I get a pretty solid 16-17mpg from a 2.8L, automatic in mixed driving. I have a heavy foot. (adjusted for tire size increase)

Jill's got an 87 XJ with auto trans and 4.0L , with me driving it gets about 18-19mpg. (also adjusted for tire size increase) I don't know what mileage it gets with her driving, as she never keeps track of that.