got a 99 suburban 196K miles, getting crumby gas mileage +/- 9 miles to the gallon lately any suggestions to improve gas mileage. when should the gas filter be replaced?
A suburban, of course, just gets terrible gas mileage to begin with.
No one knows where to start b/c you haven’t said anything about the vehicle. But you ask about the fuel filter. Start by pulling out the maintenance schedule for the truck & getting everything up to date. I have to assume its not up to date or you wouldn’t be asking about the fuel filter. So worry about that, and spark plugs & wires & air filter.
Remove anything unnecessary that makes for extra drag (e.g. roof rack).
After that worry about tires (be vigilant about pressure) and alignment.
Then worry about dragging brakes.
Then worry about your cooling system - thermostat and coolant temp sensor, especially.
A Suburban is not a high-mpg vehicle. Nobody buys one for fuel economy. All Suburban owners must pay the pump penalty for their choice.
That said, individual mpg is largely a matter of one’s driving habits. If you spend most of your driving doing errands about town, 9 mpg is to be expected. Nothing will improve your fuel economy as long as this is your normal usage.
The maintenance tips provided by cigroller above are surely recommended in any case. Just don’t expect a significant increase in mpg. Decide instead whether you want to keep your Suburban or trade it in for a more fuel-efficient vehicle.
Sometimes I wonder if these folks who say, “I drive a huge gas hog and want to get better fuel economy” are trolls, trying to elicit a reaction from people like me.
I shall resist the urge to say, “You should have known better.” and instead, I shall say, “I regret to inform you that you must either live with your choice to drive a behemoth of a vehicle, or find an alternative vehicle. Regarding the vehicle you have now, you cannot change the laws of physics.”
Righto - I always forget to mention that the biggest variable is the nut behind the wheel (and on the throttle)
I think there are people out there who genuinely believe they can somehow magically force a vehicle that large, heavy and with a motor of that size to get a nice cool 23MPG, or even better.
We’ve all seen them. They merge onto a busy highway where everyone’s doing 70 aand they’re crawling along at 35. Or take so long to go through an intersection the light changes when they’re halfway through. 
I geuss if we remove the entirety of the interior, cut the body down to that of a pickup cab, and find some way to eliminate a great majoruty of the chassis weight, it may be possible. Oh, and install pedals and a chain drive.
All that cigroller sez, plus:
Change the thermostat every 5 years.
Use the thinnest recommended oil.
Drive as if there’s a raw egg between your foot and the accelerator.
I do agree that this kind of inquiry is nuts. I generally assume, however, that OPs are asking about changes for the worse in terms of what they are accustomed to. Maybe the OP used to get a whopping 12 mpg
9 mpg is off from what I have been told by customers (give the EPA specs. a check out and see how far off you are). With standard size tires my experience says city driving should give you 12 but give the official ratings a look over.
What you need to do is buy a second vehicle to take the load and miles off of your precious truck.
Lets say that your truck gets 12 mpg on your normal commute to and from work, which is 55 miles each day. With a 5 day work week, and 50 weeks you have to drive to work every year, you have traveled 13,750 miles. That means that you need to buy and burn just under 1146 gallons of gasoline.
Lets say that fuel is $4 per gallon right now where you live.
That means you spend $4584 to drive your truck every year.
Now, lets change your truck over to a motorcycle that gets 50 mpg.
Lets say that you can use it 1/2 the time instead of your truck.
That’s 6,875 miles in a year.
That only needs 137.5 gallons of gas ($550) to get where it’s going, and your truck burns 573 gallons of gas ($2292). This means you just saved $1742 in fuel costs. If you drive the bike more, you save even more money, of course.
If you make the bike do 3/4 of the miles for your commute, you save
$825 for the bike’s fuel tank, $1145 for the truck, which equals a $2614 savings.
So, go find yourself an inexpensive bike, get some insurance, some riding gear, and start saving a real amount of money, instead of trying to make your truck do something it just can’t.
BC.
I’ll echo Whitey’s comments
That’s low, even for a Suburban 1500 woth 2WD. Revised EPA estimates are 12 city and 17 highway. Individuals report mileage as low as 12 MPG with 80 city driving. You can see the resuts at fueleconomy.gov. If you have a 2500 and/or 4WD, that will decrease gas mileage. I suppose you might also have the 6.5L diesel, and that might affect mileage as well. Replace the air filter and make sure your tires are inflated to the proper pressure. It should be on a plate on the door sill. Did you ever replace the spark plugs? It might be time for that, too. It couldn’t hurt to replace the fuel filter on an 11 year old truck, but I’d expect it to run rough it is is clogged.
without knowing what type of driving is done, 9mpg may be a good number. My car is rated 17/24, but I’ve been lucky to get 15mpg due to my type of driving(~3 mile one way trip to work/store), winter cost me 1 or 2 mpg mostly due to using the remote starter.
People post their mileage on that site. The worst reported was 12 MPG. OPs mileage may be because of the way he drives, but he would still have the worst reported mileage by a long shot.