If your commute is only 6 miles long,
consider getting an electric block heater
and an electric timer to turn the power to the heat on about 2 hrs before you drive.

If the troublesome original Chrysler lean burn system
is 'long gone'
and if you are still willing to spend some $ for improved MPG
consider getting a
Chrysler 318 or 360 TBI throttle body & manifold
from a salvage yard
and for control connect it to a moderate cost MegaSquirt ECM
using a wide range oxygen sensor
to correctly control the air to fuel ratio.

My guess is that this type of modernized
'Lean Burn' system
would give about a
4 MPG gain in city driving,
and perhaps more at highway cruise.

In addition
with the flip of a few switches
the settings could be changed inside the MegaSquirt to a maximum horsepower tune
with revised a/f and ignition timing.
Forty to fifty added horsepower might be a ball park guess of the gain of such a tune... even more if this performance tune was for E85 fuel.

If you are getting 17 mpg on a 6 mile commute in the city.

You need to post on what YOU are doing, not asking us!

With number like that. I'm assuming you are already well versed at vacuum advance.

I have a set of small advance springs I want to try but have not gotten around to it..have bumped initial timing 5 degrees over stock till then.

honestly, 17mpg in that commute in an M body is doing pretty good. I can't think of anything cheap to significantly improve this.

if you wanted to spend some coin, maybe try duplicate hotroddave's fuel economy build.....or at the very least, a 4bbl intake with a small q-jet or t-quad might give 1-2mpg better mileage than the carter BBD 2bbl you probably have, as long as you keep out of the secondaries.

A 6 mile commute with those numbers is very good.
It sounds like you are getting about as much as possible now, so improvements from here are going to be tougher.
I'd suggest trying synthetic lubes, an alignment, and decreasing the rolling resistance.
What tires and pressures are you running?

As mentioned, there are engine changes that can help, but at what cost? Raising the compression and installing EFI will cost ten times the 152 buck savings, when you consider tuning, gaskets and fluids and the parts. If you do go inside the engine, I'd also look at coatings.

What engine temps are you seeing? Late model stuff is run very warm. If your cooling system can handle it, running warmer can get more MPG.

Just changed rear end fluid to redline 75-90 synthetic, will have to wait for results. Tires are cheap but narrow tread 205/75/15's with 45PSI front and 40PSI rear

Here's a graph from the internet archive (Wayback Machine) where the U of Florida did an experiment with short city driving style commutes:

http://web.archive.org/web/2006050719451...nce-500x361.jpg

the full archive of the original webpage
which has more advice on improving MPG
is at

http://web.archive.org/web/20060507194510/http://www.fsec.ucf.edu/Pubs/energynotes/en-19.htm

if you have a six mile commute, get a bike