Took the truck on vacation last week and was pleased with how it did on fuel. This is a stock 2007 2WD CCSB 5.3 LMG with AFM. Only mods are an S&B intake and a Spin Tech muffler welded in place of the stocker. Stock tailpipe and all. Lowered 2/3 with struts/shackles/block delete with stock size 20's and a soft bed cover, the truck has never been tuned. We had 3 adults, one child, the bed was loaded to the rails, extra spare tire, hyd jack, tools, etc... We were loaded down heavy enough that I could feel the weight leaving a light, never weighed the truck loaded though. It weighed about 5100 empty, I'm guessing we were well over 6K.

We Left SE Texas and went thru LA, MS, AL, GA and stopped for the night close to Charleston, SC. Drove thru rain the entire first two days of the trip and averaged speeds around 72-74mph. We drove thru mostly flat terrain with some rolling hills thru GA and SC. We ended up with 18-18.5MPG the whole way first day. I'm guessing it was due to the constant winds we were bucking through those storms.

Second day we went thru SC, NC, into VA and took a detour over to VA Beach to see some friends and have dinner before finishing out trip to the DC area. The first fill-up showed almost 19mpg with the same speed thru steeper and longer hills. Figured it several times and got the same result, second tank showed 19.6mpg, but I figured that was about right given the slows speeds thru The back roads of VA, almost everything is 55mph. I never exceeded 60.

Spent the whole following week in DC traffic, idling thru parking garages, trying not to die basically. Crazy bastards up that way... We managed 16-17mpg mixed driving since we were actually staying outside DC in northern VA, which is about what I expected.

Started the trip home and drive thru western VA, eastern TN, and into northern AL. The Smoky Mountains. The speed limits varied but we drove anywhere from 60-65 up to 73ish. The first tank showed 19.6mpg, and got BETTER as we entered the mountains. Filled up again in TN and ended up with 20.4mpg. We stayed in Tuscaloosa, AL after the day of driving.

Topped the truck off before getting back on the rd and showed to be getting the same 20.3-20.4mpg for that tank as well. The last day took us thru AL, MS, LA and back into TX. I pretty much drove 75mph the entire day and the mileage never really dropped. Still stayed high 19's the whole trip back. Filled up at home and showed 20 on the dot...

My conclusions are that the AFM system really does help on long coasting hills more than it does on flatter ground, especially in a heavy truck. I had to add a qt of oil about 2500mi into the trip but I also expected that. The oil change had 5000mi on it at that point and that's been about normal since I've owned it. It also rolled over 100K somewhere in the Smoky Mountains.

Anyway, long winded as usual. But that's as accurate as I can make it without going full retard. Just putting it out there if someone was possibly planning a similar type of trip or having questions about what they should expect.

 

Thats awesome. Our T70 equipped 2010 5.3 cc averages about 18.4 from San Anto to Houston if we stay out of boost so i can see where yours get 20+. My cammed 4.8 with 4.10s only gets about 14.1 mpgs though

 

I was pretty happy with it. Like I said this is a 99% stock 5.3/4L70E/3.23 truck with 275/55/20's. At 75mph it turns about 1800.

I was more pleased with how it handled the mountains being that heavy. It did unlock the converter and even dropped into 3rd a time or two but never felt like it was in a bad bind. You could just hear the exhaust get a little deeper and it went on up the hill

 

Those are good results. My 2011 CCSB 4.8L 4wd only averaged about 15-17mpg highway from deep South Tx to San Diego, Ca then to Las Vegas and back. Truck got great mileage on the flat straights but any hill and the truck struggled to stay at speed. Noticed it a lot in Nevada when minivans were passing me on some steep uphill roads.

 

VERY NICE!! I do all city driving in my 08 RCSB 4.8 with 3.73's. I actually go through 19 lights in 13 miles one way. I average 14.8-15.0 driving sprinitedly! Never made a highway trip in it.

 

Pfft my 2000 z71 cinsistantly avg 13 :/