You need a little bit more info than you are giving (the original MPG). Normalize (find) your cost per mile, get the difference on adding the new technology, then compare to the price of the new technology.
Here would be the formula:
Technology_Cost/( (Gasoline_Cost/Original_MPG) - (Gasoline_Cost/New_MPG) )
so at $4/gal, $1500 for technology, increasing MPG from 25 --> 30.
1500/((4/25)-(4/30)) ---> 56250 miles.
10 ---> 15 = 11250 miles
15 ---> 20 = 22500 miles
20 ---> 25 = 37500 miles
25 ---> 30 = 56250 miles
30 ---> 35 = 78750 miles
35 ---> 40 = 105000 miles
40 ---> 45 = 135000 miles
45 ---> 50 = 168750 miles
50 ---> 55 = 206250 miles
You can see that adding technology to a truck or SUV to increase MPG will really pay off compared to a small car. I'd expect the technology costs to be more than you have and the increased MPG to be less than you have also.