Going to fueleconomy (dot) gov and checking a 1991 Sentra gives the following (using the new method that is lower than the old rating method) 1.6 Auto 23 C / 33 H, 1.6 Manual 25 / 35. The 2.0 Auto 20 / 27, 2.0 Manual 21 / 29.
I personally find it easy to drive in such a fashion with a manual to easily beat the EPA numbers.
Not so easy to make a big improvement on the automatic numbers for me. I don't like kicking an automatic into neutral to coast and then back into drive at near highway speeds.
Good luck in your search.