I get 32+ mpg with 92 Lumina

I have a 1992 Lumina with 3.1L V6 engine and 4 speed auto trans. It is the 4 door sedan. When I drive on the interstate going 70 mph I get 32-35 mpg. What is weird though is if I drive 55 mph on state highways I only get about 28 mpg.

I keep my car tuned up, maintaned, and keep the tire pressure up, and here is what else I have done:

K&N filter
Slick 50 oil treatment
Tornado gas saver

I don't know how much the Tornado contributes to the good mileage. Maybe it only works good at the higher speeds.
Anyone else use one of those with success?

I use Castrol Syntec Blend w/NAPA filters. Not unusual mileage for these autos if running good oil and tune-up, proper tire inflation, clean filters,etc.
The reason for the drop @lower speed is the gear ratio in that OD. trans with factory tire size. If most of driving is on 55 or less roads, drop 1 profile size (70 to 65)but keep same width (205, 195...) for handling. These will do better in lower speed situations as the engine will not have to work as hard.

I tend not to waste my time/money on anything that's "too good to be true"...because it IS. However, I've haven't heard anything neither good nor bad about the tornado.

Take off the Tornado and see what your gas mileage is then.