how far do you commute? (2way)

daily driver?  

about 20 km  

Well my Malibu makes two trips to work each day. Around 11 miles to one job and back. Around 15 to the other one and back. Mostly city driving, but my engine seems to like any speed under 55 MPH. I can avg almost 27 MPG outta that 267 all freeway if I stay under 55 MPH, the minute I cruise at 65 MPH, it drops to a low 19 MPG. Must be from RPMs and stock camshaft.  

Being a in the building trades I go from job to job. The closest has been 1/2 mile the farthest is 75 miles all 1 way any farther than that I'll find a place to stay as close to the work site as I can.  

The reason your Malibu loses mileage above 55, the cam in the motor loses vacuum at higher RPM/MPH, and whenever vacuum drops, so will mileage.

To verify this, get yourself a vacuum gauge and hook it up to the motor, and watch what the vacuum does from 55 MPH up.

A cam change would probably do wonders for even this anemic small block. A very mild hydraulic roller that'll pull good vacuum at higher engine speeds than the stock cam.  

2hrs to work 2hrs home. All in my 13 mpg, 2500 Chevy 6.0L  

55_Hardtop_Guy:
The reason your Malibu loses mileage above 55, the cam in the motor loses vacuum at higher RPM/MPH, and whenever vacuum drops, so will mileage.

To verify this, get yourself a vacuum gauge and hook it up to the motor, and watch what the vacuum does from 55 MPH up.

A cam change would probably do wonders for even this anemic small block. A very mild hydraulic roller that'll pull good vacuum at higher engine speeds than the stock cam.

That's what I was thinking. My peak torque is at 2400 Rpm, meaning my Vacuum is probably highest at that point. That is also around the engine speed I'd be running with my dummy converter at 55 MPH. I have an Edebrock performer series intake and a matching cam to go on the engine. Edelbrock advertises that their perforer package, NOT the RPM pakage, is designed to generate peak torque around 3500 RPM.