Why does my tahoe use so much gas - 1999 Chevrolet Cavalier

Fuel injector problem , leaking fuel pressure regulator ,

Causes of gas in oil
On my 94 Chevy blazer, gas in the oil was caused by a ruptured diaphragm in the fuel pressure regulator that is attached to the fuel injector. Flooding the engine. An over abundance of gas in your cylinders will wash down your cylinder walls and accumulate in the oil pan.

Your fuel pressure can be checked by connecting a fuel test gauge up to fuel test port which will be located on the fuel rail at the back of the engine on drivers side next to the distributor.Your fuel pressure should be 60-66 psi with key on engine off.If its not within these specs then replace the fuel pump and filter.

If your Tahoe is the 5.3 Non flex fuel then its in the gas tank then you dont replace it.
It's supposed to last the life of the Tahoe.
If your Tahoe is the 5.3 flex then the fuel filter is located on the under carriage of the frame and should be replaced every 15,000 miles.

I prefer bosch plugs :

2000 Chevrolet Tahoe 5.3L 323CID V8 GAS FI T - GAP=0.040"; Original equipment is iridium. 2000 Chevrolet Tahoe 4.8L 294CID V8 GAS FI V - GAP=0.040"; Original equipment is iridium. 2001 Chevrolet Tahoe 5.3L 323CID V8 GAS FI T - GAP=0.040"; Original equipment is iridium. 2001 Chevrolet Tahoe 4.8L 294CID V8 GAS FI V - GAP=0.040"; Original equipment is iridium. 2002 Chevrolet Tahoe 5.3L 323CID V8 FLEX FI Z - GAP=0.040"; Original equipment is iridium. 2002 Chevrolet Tahoe 5.3L 323CID V8 GAS FI T - GAP=0.040"; Original equipment is iridium. 2002 Chevrolet Tahoe 4.8L 294CID V8 GAS FI V - GAP=0.040"; Original equipment is iridium. 2003 Chevrolet Tahoe 5.3L 323CID V8 FLEX FI Z - GAP=0.040"; Original equipment is iridium. 2003 Chevrolet Tahoe 5.3L 323CID V8 GAS FI T - GAP=0.040"; Original equipment is iridium. 2003 Chevrolet Tahoe 4.8L 294CID V8 GAS FI V - GAP=0.040"; Original equipment is iridium. 2004 Chevrolet Tahoe 5.3L 323CID V8 FLEX FI Z - GAP=0.040"; Original equipment is iridium. 2004 Chevrolet Tahoe 5.3L 323CID V8 GAS FI T - GAP=0.040"; Original equipment is iridium. 2004 Chevrolet Tahoe 4.8L 294CID V8 GAS FI V - GAP=0.040"; Original equipment is iridium. 2005 Chevrolet Tahoe LS 5.3L 323CID V8 FLEX FI Z - GAP=0.040"; Original equipment is iridium. 2005 Chevrolet Tahoe LS 5.3L 323CID V8 GAS FI T - GAP=0.040"; Original equipment is iridium. 2005 Chevrolet Tahoe LS 4.8L 294CID V8 GAS FI V - GAP=0.040"; Original equipment is iridium. 2005 Chevrolet Tahoe LT 5.3L 323CID V8 FLEX FI Z - GAP=0.040"; Original equipment is iridium. 2005 Chevrolet Tahoe LT 5.3L 323CID V8 GAS FI T - GAP=0.040"; Original equipment is iridium. 2005 Chevrolet Tahoe Z71 5.3L 323CID V8 FLEX FI Z - GAP=0.040"; Original equipment is iridium. 2005 Chevrolet Tahoe Z71 5.3L 323CID V8 GAS FI T - GAP=0.040"; Original equipment is iridium. 2006 Chevrolet Tahoe 5.3L 5328CC 325CID V8 FLEX FI Z L59 - GAP=0.040"; Original equipment is iridium. 2006 Chevrolet Tahoe 5.3L 325CID V8 GAS FI T - GAP=0.040"; Original equipment is iridium. 2006 Chevrolet Tahoe 4.8L 294CID V8 GAS FI V - GAP=0.040"; Original equipment is iridium. 2006 Chevrolet Tahoe LS 5.3L 5328CC 325CID V8 FLEX FI Z L59 - GAP=0.040"; Original equipment is iridium. 2006 Chevrolet Tahoe LS 5.3L 325CID V8 GAS FI T - GAP=0.040"; Original equipment is iridium. 2006 Chevrolet Tahoe LS 4.8L 294CID V8 GAS FI V - GAP=0.040"; Original equipment is iridium. 2006 Chevrolet Tahoe LT 5.3L 5328CC 325CID V8 FLEX FI Z L59 - GAP=0.040"; Original equipment is iridium. 2006 Chevrolet Tahoe LT 5.3L 325CID V8 GAS FI T - GAP=0.040"; Original equipment is iridium. 2006 Chevrolet Tahoe Z71 5.3L 5328CC 325CID V8 FLEX FI Z L59 - GAP=0.040"; Original equipment is iridium. 2006 Chevrolet Tahoe Z71 5.3L 325CID V8 GAS FI T - GAP=0.040"; Original equipment is iridium. 2007 Chevrolet Tahoe LS 4.8L 294CID V8 GAS FI C - GAP=0.040"; Original equipment is iridium. 2007 Chevrolet Tahoe LS 5.3L 5328CC 325CID V8 GAS FI J LY5 - GAP=0.040"; Original equipment is iridium. 2007 Chevrolet Tahoe LT 5.3L 5328CC 325CID V8 GAS FI J LY5 - GAP=0.040"; Original equipment is iridium. 2007 Chevrolet Tahoe LTZ 5.3L 5328CC 325CID V8 GAS FI J LY5 - GAP=0.040"; Original equipment is iridium

fuel filter should be in gas line comming from the tank.
will be close to tank on either drivers side or passenger side.in front of back wheels.

Check HERE for Gas engine:
Make: CHEVROLET
Model: TAHOE
Year: 1999
Engine: V8 - 5.7L - FI - - GAS

Good luck (remember rated this help).

May be nothing more than a faulty gas cap or vent hose from the tank to the filler neck. Your charcoal canister for the fuel evaporation system may not be purging. It could be filling up with gas. It will eventually overflow, allowing you to see the problem.

fuelpump fuel filter fuelregulater or bad gas maybe leak in top of two piece manafold

Have a dealer or garage check your Oxygen (O2) sensor. As a quick fix, try disconnecting and reconnecting your car battery. Sometimes this will reset the check engine light.Good Luck!

bad gas ,water in the gas