9 mpg is normal for driving with a heavy foot... your idea of not having a heavy foot might be a bit more than others.. just throwing that out there as a possibility and maybe your missing oil isnt all from the leaky gasket.
how long since a tuneup was done?

 

well the times i have calculated the mpg i wasn't driving with a lead foot tho.. got another oil change in 500 miles and did plugs and distributor cap and rotor 5 months ago

 

clould it be because my front o2 sensor is a ntk and rear is a bosch? if the timing is advanced would that cause bad gas mileage

 

these trucks hate bosch, but the rear doesnt do much with the MPGs. its just says whether your cat is working or not. and timing wouldnt be a factor on these trucks. even if the timing would make a difference, theres nothing you can do about it on these trucks. all ignition timing is contolled by the PCM. some techs think that you can control it with the dizzy but you cant. that controls the trucks fuel sync.

 

Oddly enough, I was just looking at that setting on my tuner this afternoon when I backed the base timing off, back to the tuner's default setting for 91 octane/performance.

 

Not thats it's truly worth it but there alot of talk going on about 0 ohm spark-plug wires. They seem to boost performance and mpgs. Also you could boost your mileage by filling your tires with nitrogen instead of air. I had a bud who did that and it kicked up his mpgs 2-4 mpg.

 

Any/all fuel economy gains with nitrogen are due to the fact that the tires were underinflated before some guy put in some expensive gas and those cute green caps on your valve stems. That's 100% of the effect. You can get the same benefit by checking/adjusting your tire pressure once each month like the owner's manual says you should.

Zero ohm wires, well... the pink unicorns seem to like 'em just fine but the flying dragons think they taste just like chicken, and dragons don't like chicken.

 

Somin around 14 mpgs should be able to be reached even without the magical products on the market. If it were me I would make FOR SURE the plenum isn't leakin and make sure your cat isnt clogged and such. If you haven't replaced the front O2 since you've owned it, i would replace it. Jus my 2 cents

 

Light foot = well under 2k rpm (for me at least, I try to stay under 1800...its gotten me as much as 22mpg highway, 2wd and nothing extra in the truck, shed as much weight as possible)

 

I run an exotic blend of about 78% nitrogen, 20% oxygen, and the last 2% a mixture of water vapor, CO2, trace hydrogen and various noble gasses.

Works pretty well as long as the pressure is regulated well at the optimal level.