My rough calculations give me high 20s low 30s highway in my 95 LT1 6 speed. I only calculated city once, when I first got the car, at 11 MPG. I wasn't exactly driving conservitavly though. A friend of mine consistantly gets 32 highway in his Trans Am (6 speed LT1). He also has well over 400 HP on the dyno, and I've got a fairly agressive cam and 3.73s myself.

 

I get about 24-27 in my 3.8 on back roads in the country. About 20 in town.