I hang out in a couple of Sunfire groups and have never heard of a V6 swap. I guess it might be "possible", but it may or may not be worth what it takes to get it done. I've wished for a long time, that Pontiac had offered a 6 cylinder engine for Sunfires.
My '96 averaged from 26 to 32 MPG, depending on how I drove her and upon conditions. Most often, I averaged around 27 to 28+. And this was when the car had 225,000 miles on the OD.
Motorweek - 1987 Pontiac G8 GXP 28-28 was released on: USA: 13 March 2009
The Stephanie Miller Show - 1995 1995-09-28 was released on: USA: 28 September 1995
28 February 1995 was a Tuesday.
30 psi front and 28 psi rear is good.
Depending on the usual variables, like speed driven, road conditions, wind, AC on or not, my '96 with 213,000 miles on the clock still gets between 28 and 32 mpg. Maybe that will give you some idea what to expect.
April 28. 1995 fell on a Friday.
December 28, 1995 fell on a Thursday.
MisteRogers' Neighborhood - 1968 1995-08-28 was released on: USA: 28 August 1995
Politically Incorrect - 1993 1995-03-28 was released on: USA: 28 March 1995
Praise the Lord - 1973 1995-03-28 was released on: USA: 28 March 1995
CBS This Morning - 1987 1995-08-28 was released on: USA: 28 August 1995