Of course...

[Shdwdrgn]

Now that I've changed over to 4.10's, I'm taking a road trip to Iowa tomorrow. This will be the first time I've driven more than a couple hours on the highway since I got the vehicle. It should be interesting to see what my gas mileage looks like by the time I get back though -- I've been creeping into the 15's as the weather has been getting warmer, but 90% of my driving is back & forth to work in a lot of traffic. I've been wanting to take a road trip ever since I got my TB, so I'm excited!

So... fluids are topped off, checked the spare tire, have a few tools in back for emergencies. I think I'm ready to go. Also may have a chance for another GM tech to take a hands-on look at my PCM situation, so the spare is also packed away. Wish me luck!

[navigator]

Jeff, did you notice much difference in gas mileage for your short trips after going up to 4.10s?
I'm about ready to install my new 4.10 diffs and figure I might see a small bump up on short DD trips and a drop on longer trips.

[Shdwdrgn]

Honestly I was expecting a bump *up* in mileage because I do so much in-town driving, but no - so far I have not seen any improvements. I installed the gears as the temperatures were dropping, and thus my mileage also dropped for the Winter. Last Summer I averaging in the upper-15's and sometimes even getting into the lower 16's for my daily drive, despite the fact that I was normally driving in 3rd gear for better speed control in traffic. With the new gears I can comfortably leave it in drive all the time, which should still be a lower ratio than running the 3.42's in 3rd, but I am still not seeing the mileage. If I were to guess, I would start with looking at the PCM to see if I missed modifying anything that would affect the economy.

I'm driving from Colorado to Iowa, downhill all the way... If everything goes well and I am able to get the PCM reprogrammed while there (and I'm taking my laptop along so I can then change the stock settings back to my modified settings), it would be very interesting to see if I get any better mileage on the trip back home...

[navigator]

good luck.

[HARDTRAILZ]

My biggest gain was highway due to better tc lockup

[Shdwdrgn]

So we didn't have a chance to do the PCM reprogramming, but I still have an appointment here in Thursday...

Gas mileage appears to have been (assuming I didn't lose any receipts) 19.0mpg going to Iowa, and 13.1mpg coming back (with a truck load of boxes). Average for the whole trip was 15.0mpg... which sucks since my normal stop&go daily drive gets me about 15.2.

Then again, the truck cruised really well at 85mph on the highway. Of course it cruised really well at 95mph also, but the cop wasn't as impressed...

[Trail X]

85 mph is why you got such crappy mileage.

[Shdwdrgn]

85 mph is why you got such crappy mileage.

but but but ... I got there really fast!!!

[KingBird]

Yeah, we normally see around 16.5 on the highway, except for this last trip, we had an appointment at home, and we didn't leave our vacation spot 3.5 hours away until 3.5 hours before the appointment, with a five month old that needed to feed halfway there. In my 'vette I made the same trip in three hours three minutes, averaged 75mph including a fifteen minute stop for gas. In the Bravada we made it in three hours fifteen minutes with the same stop. Gas mileage averaged about 14.5...

[HARDTRAILZ]

In 1 hour at 110 mph I got 11.43 mpg. At 55 mpg for 2 hr I got 21.27 mpg

[Shdwdrgn]

I was running about 95 for maybe 1/3 of the downhill trip, and then only backed off to around 83mph for the rest of that trip, and got noticeably better mileage than the return trip where I was trying to keep it just under 85 the whole way. Nothing was strapped on the luggage rack, and the boxes I brought back weren't all that heavy (well under 150 pounds, maybe under 100). So I dunno?

[Trail X]

The drag is related to velocity by a power of 2. So the drag force actually increases by 25% between 85 mph and 95 mph. The difference between 70 mph and 95 mph is a 84% increase in drag.

This is why driving into a 15 or 20 mph headwind can really kill your gas mileage.

[Shdwdrgn]

Speaking of wind... we ran into a killer cross-wind all the way across Nebraska and Western Iowa, going both directions. Probably saw gusts over 50mph in some places, and that made the driving all that much more fun (not to mention the effect it had on my mileage, I'm sure). Regardless, the truck had no complaints for the entire trip. She just kept right on going smoothly down the road. I'll have to check my fluid levels again this weekend, and I know its about time to change the transmission fluid, but I'm really happy with the trip. If you're not critical of your gas mileage, this truck makes one hell of an all-purpose vehicle.