So at first I seemed to get 10 around town. Put in the new air intake and DennyT fuel pin and I seem to get about 12 around town. Just drove 8 hours to Northern Cal and back. 70mph at 1700RPM, Between 5 and 600 on the Pyro in the heat of the valley. Pyro is in the downpipe. The gas gauge was amazingly slow. 300 miles and it was just past the half full mark. 18.3 mpg. Half a tamk is really just past the half way mark as when I filled it up it took 15 gal. Gas left if I run it down to the low fuel light is between 7 and 8 gallons left in the tank.

Just got a Geno's "FSM" CD. Comes with some literature about "Frequently asked questions". It says "Regardless of the year/model of the truck, you can expect:

12-18 mpg - without a load
9-13 mpg - with a load

If t his is the case it seems that I am right in the ballpark.

 

That sounds more like it. 18.3 is good for that big truck...But it doesn't count because you have a good converter and most of us don't

I have no idea why your truck was getting 12 and 10mpg for a while.. and all of a sudden it goes to 18 like its supposed to.. our non i/c truck with no overdrive gets 18mpg running 65.

Whats your cruising boost??

 

18.5 is what mine's always gotten at 70, so your results sound normal. If I slow down to 60 it will get 20 mpg.

 

Seemed to run between 5 and 7 cruising at 70. You funny sometimes Brandon. That 18 is on the highway. More like 12 in town. My town compared to your town has a stop sign at the end of almost every block. Signals every quarter mile. That's probably why it's so low. Takes a bit to get that "big truck" rollin and stoppin over and over and over again.

 

I'm sure you don't roll out any coal when you take off either I always say im gonna try not to do that taking off and see how good of mileage i can really get. It never seems to happen. I'm not too dissapointed with 22MPG at 70 MPH though.

 

Like Wanna said, slowing down a little will help a LOT. Air resistance is exponential above 55mph, and the number one drag on the vehicle at that speed. Since we have the aerodynamics of... well... a barn, it matters a lot for us!

In my W350 with a stock converter and DRW (new injectors and timing advanced) I get 17.5 at 70mph, but almost 20 at 60-65mph. That's with a major boost leak too.

Advancing the timing 1/8th of an inch really helps. the fuel and mid range power like pulling hills. Little more clatter at idle, but the positive side is great!

 

Just drove 4 consecutive 270 mile round trips averaging 65mph and 20.5 mpg. My mileage definitely went up about 2 mpg after I did the timing bump. City driving or towing usually 18 mpg.

 

If someone pushed my 92 with the 4:10s and the auto I might get 20 mpg. 4:10s auto and a GV od I get 13.87 on the hiway at 7 to 9 lbs of boost. You guys must have 3:54s and a good convertor.

 

I get ~17.5 at 70 with my 93 CC 4x4 with 4.10 and really aggressive mud tires.

 

My last fill was 20.56 MPG wih about 50/50 city freeway driving. That is what I've seen since low sulfur Diesel came on the market. The freeway is at 60 MPH and is heavily patrolled by both OR and WA. I keep my speed on rural interstates at 65 and have seen a 2 to 3 MPG increase over mileage at 65 to 70 MPH. When I make a run from Portland OR to Meridian ID it takes me about 15 to 30 minutes longer to run that 450 miles at 65MPH.

Bob

 

with what's in my sig if I keep it around 60-65 I'll get 18-19 mpg or so. Stock converter too.

I find that if I drive around town my mileage goes WAY down and if I drive in town a lot it progressively gets worse. Last winter was a good example. I drove for a couple months almost exclusively in town and within a couple weeks my mileage was around 10 mpg and never got any better than that really. And for a little while my highway mileage was aweful after that too. These trucks really don't like city driving. The engine really seems to like cruising on the highway or driving with a load behind it.

 

That sounds like mine. By best has been 22 but usually its about 20-21 at 60-65mph. But at 70-75 it drops down to 17.5-18.5.

It also depends on traffic for me too.