My father in law and brother in law both own Z-71's x-cabs with the 5.3l. Both claim to average 17 or 18 city and 19 to 21 hwy.
I get 13 to 15.1 city and hwy.
I did'nt buy the truck to get good mpg. But hey I would at least like to get above 15 mpg.

 

I have noticed the same thing with older motors. My 302 gets worse mileage than many GM 350s do. Of course, when I say anything about that here, everybody thinks that there is something wrong with my motor, when everybody that I know gets the same mpg with their 302.

 

but when it comes time to tow with your 5.4, you will have a lot more torque. Ford motors have a lot more low end torque than the equivlent chevy. Would really can not have good low end torque and good milage, the best i have gotten with an engine with good low end torque, besides my 300, was 13 out of my 390. I have a 5.7 chebbie 2500, and that thing has no low end torque. Off the line it sucks, once you hit 3500 rpm then it takes off. Reminds me of a high winding rice burner.

 

Is it a Vortec or TB? The Vortecs do not lug as well. I know some who pulls a 12,000 lb loaded 20' stock trailer with a 1/2 ton Chevy, 5.3l, and it does pretty well. I'm not saying that it would pull better than a 5.4, but it pulls well.

 

mjd, in all likeyhood you do have something wrong with you 302. if you saw towinbobs post he gets 19 going 60 in his 302. it is to general of stament to say that chevys in general get better mileage than fords. what does the 5.3L vortec get on the highway? the ford 5.4L gets about 19-20 on the highway i beleive.

 

If I have something wrong with my motor, then everyone that I know does too. I go 75 mph, not 60.

 

My 5.8 only gets 10mpg. I don't care what the conditions are. If fords have more torque, they should use less gas. Torque gets the load moving. I love my truck, but I had an 87 silverado4x4 350, auto w/4.10's and got 14 in town and 22 on the road and it would pull a builing down.

 

19-20 mpg! Try 10-15. My 5.4 is a gas hog.

 

also chevys rear end gearing is differnt than fords till you get to a 3.73. chevy has a 3.42 and ford has a 3.55. that will effect the mialge a little as well

 

My pickup was only available with a 3.08, 3.55 and 4.10 gear ratio. I think that I would make slightly better mileage with 3.73 instead of 3.55 ratio because it would probably be able to pull hills in cruise without shifting and would pull against the wind better. Part of the reason that 302s do not make very good mpg is because they struggle too much. 3.08s would literally be a nightmare in my pickup. 3.55 and 3.42 gear ratios are too high for a SB gas engine. The 3.73 gear ratio is perfect for a pickup like mine, but Ford did not offer it. The difference is small between 3.55 and 3.73, but it makes a big difference. If you have a stick-shift, it will add life to the clutch also. 3.55s are ok with a diesel, but thats about it.

 

Just FYI, my 2002 5.3L 2wd Ext Cab Sierra SLE with 3.73s typically gets ~17mpg mixed driving. Lately doing short trips in damn cold weather I'm getting only 15mpg. Best I've ever seen is about 18mpg.

Definitely a little shy of bottom end grunt (ie, <2000rpm) and the tranny is garbage, but above 2000rpm on the open road it pulls my 8000lbs enclosed car trailer at 130kph (>80mph... assuming no headwind) and still gets 9mpg.

All said... I'm still trying to sell it to buy a 6L PSD F350... because... 9mpg is not 13mpg, and 325lb-ft is not 560.

 

my observation is - for similar size motor, ford has more torque than a GM. torque needs fuel, just the way it is, even when not hauling anything.

 

Yeah, 3.55's are a waste in a truck the size of mine. It does fine pulling up to about 8000 pounds, but it still only gets 10-12 mpg. I have been playing around with a 3.73 or 4.10 swap in my mind, but nothing has sold me on it yet. It seems the 3.55's make it hard for my transmission to decide whether to stay in 4th or drop into 3rd in the 35mph zones around here. However, I have heard that 460's get the same mpg regardless of the gearing.

 

I owned a 2001 Silverado 1500 ext cab Z71 with 5.3L and 4.10s and it only averaged 13/14 mpg. I talked to a few guys who had the same configuration GM 1500s and they would say they were getting 18/20 mpg...they are fibbing.


BTW-that truck towed just fine for a 1/2 ton. I revved high but you could maintain 65/70mpg with a 4000lb trailer on all but the longest grades.

 

In carbed motors i don't know how torque affects gas mileage when its based of rpm and the cam eccentric. And i always here 302 owners complaining about gas mileage. most get around 12 from what i have heard. the gm high rpm power reminds me when i was driving a 350 chevy and in 2nd gear it couldn't get up a slight incline.