CUBFXR

My wife has an 06 tahoe with 5.3L engine -139,000 miles.
We have noticed a huge drop in mileage over the last year.
Used to get close to 18 on highway and 14 to 15 city.
We are down to 10.3 city and barely 14 on last road trip.
Set tire psi, changed plugs and harness, replaced air filter, cleaned injection system and have been all over truck looking for any sign of fuel leaks.
Seems to use even alot more idling than it use to. We do live in cold climate but even summer driving was noticably poor. I realize in cold we will use more fuel but this a huge change in same conditions and with same driver. Truck runs well - no codes or misses - does feel a little more sluggish power-wise but that may be normal for the miles. I'm looking for any ideas or suggestions. Can't keep dumpling gas in with these prices...
My 07 Silverdo MAX with 6.0L is getting better mileage! - 16 mpg in same conditions. Thanks for any input.

in2pro

Are you carrying any extra weight around ?
Check the brakes to make sure they and not dragging.
How's the temp reading ? If its on the low side, it may be running rich, consider changing the t-stat.

suburbansteve3

FIRST CHECK fuel psi regulator pull vac line off key it up a few times w/o starting watch for a drop or more fuel to come out but a bad reg usually has another symptom or two mainly hard or slow start at times after that check intake gasgets there coomon togo bad usually when ther quite bad it will throw a lean code but if its still in the range where the computer can dump more fuel to satisfy o2 sensors u wont get a code if they get worse and it does throw a code mpg may go back up a bit
check them like looking 4 a vacume leak spraying brake clean or starting fluid around base of intake while listening for change in engine rpm
using a scanner that can show live data rpm and or o2 sensor data would be better than listening
BE VERRY CAREFULL UR SPAYING HIGHLY FLAMABLE FLUID OR HAVE A SHOP DO IT

CUBFXR

Thanks for ideas - I will change T-stat again - seems a little slower than normal to come up to temp - does stay steady at 195 when warm and driving.
I'll check out fuel psi - I do have a good snap-on scanner - have to figure out how to use it . I work on aircraft - still 1950's technology - magnetos and gravity feed carbs!!
Will check for intake leaks too and let you know if I figure anything out.
Thanks again

MooseII

When this happened to mine, it was a mostly clogged fuel filter.