I've been convinced that the axle ratio in my 300TE is the reason for the rpm's I have observed.

Perhaps I have a different problem here.

Let's assume for a minute given the axle ratio that I could expect 20 mpg in this car cruising at 70 on the interstate. Given a 19 gallon tank less a 2.4 gallon reserve, I'm looking at 16.6 gallons indicated on the fuel guage. At .5 tank I should expect to burn 8.3 gallons before the reserve light indicator lights up.

105 miles/8.3 gallons = 12.6 mi/gal. (observed)

Something is wrong here.

I should reasonably expect 20 mi/gal x 8.3 gallons = 166 miles before triggering reserve.

What other factors might cause this reduction in economy.

Please see my prior post -- "No top gear 300TE" from early this morning