97 sidekick issues

Have a 97 SK which is getting about 14-16mpg. Is this normal? Also, automatic tranny shifting from 2nd to 3rd is sluggish. Could be slipping in high gear? Does this tranny have an OD? If so how does one know if it is in OD or not (too much road noise over 30mph to hear anything going on)? Last thing, the front seal is leaking pretty badly. Any feedback on how much trouble this is to replace (as compared to say a GM 3.8l V6)?

tia,