Uphill Shifting Question

[Jackpine]

stl454, that mileage looks pretty good to me. I get about 12.5 mpg pulling our 3600# HiLo telescoping trailer at 65 mph. The "telescoping" feature means it has a smaller frontal area and much less wind resistance than you would have (towing height is only 72").

Habbi98, you didn't say what speed you tow at. If it's anything over 65 mph, your mileage is going to be KILLED due to the increased wind resistance and, you are really unsafe, since trailer tires are supposed to be kept to 65 mph max. I've learned a lot about trailer tires since getting our trailer, and I've got to say, I "baby" them now (also use the highest load range rated tires I can fit). The OEM Goodyear tires I had on the trailer both failed at 5000 miles within 2 years due to cord separation.

- Jack

[Habbi98]

Jack - the speed I tow at doesn't appear to be a factor in my MPG. I've towed it at 65-70max and at 55-60 and it appears to be the same either way. My dad has a 1500 GMC with a 5.3L and is getting 2-3mpg better when hauling this trailer in the same conditions. I have made minor performance mods (Headers, exhaust & Programmer) in an effort to increase the performance of my truck and it seems that it has hurt more than helped which is why it is frustrating to me. The truck has all kinds of Power on the Low End it's just at the Top End where is seems to be lacking the Power. I called Bill a couple of weeks ago and he said that it's possible that the tune may have had an issue with the programming so he is going to rewrite it and see if is any better. I hope it was just a programming issue because i can't afford <7mpg on a 1000mile round-trip haul.

[Jackpine]

Habbi - Thanks for clarifying. Things really get complicated when you try to compare the performance of one brand of truck to another, even doing identical tasks. I know I got better gas mileage pulling my trailer with my old, 6-cyl Nissan Frontier than I do with my F150, but I sure find pulling it a whole lot easier with the bigger vehicle. The combination of engine size, vehicle weight and gearing in the GMC may be making the difference.

If you have 3.55 gears, your truck doesn't have the factory tow package I think. So that, in combination with your tire size may make it hard for you to beat the GMC. Think of it this way: your truck might be "factory optimized" for "non-towing" driving. Yes, a programmer can help, but you may not be able to expect miracles.

Out of curiosity, what kind of highway mileage do you get when NOT towing? I currently get between 15.0-15.5 mpg. (This is on long Interstate trips.)

- Jack

[Habbi98]

Jack, What you said makes perfect sense. With that being the case i may look into a Gear Upgrade, to something that is a little more aggressive for towing. As I am not as concerned with my "Non-Towing" mileage because the main purpose of my truck is going to be hauling my camper. I have another vehicle for my daily driving. Any suggestions on Gear size? Would like to be able to run 33's and still have the towing power.

On the "non-towing" mileage i just went on a 600mile trip and was only able to get between 12-13mpg. Mileage was great with the Stock Program and factory manifolds (16-17mpg) but as soon as i replaced the cracked manifolds with the set of LT Headers it went south.

-Habbi-

[Jackpine]

Originally Posted by Habbi98

Jack, What you said makes perfect sense. With that being the case i may look into a Gear Upgrade, to something that is a little more aggressive for towing. As I am not as concerned with my "Non-Towing" mileage because the main purpose of my truck is going to be hauling my camper. I have another vehicle for my daily driving. Any suggestions on Gear size? Would like to be able to run 33's and still have the towing power.

On the "non-towing" mileage i just went on a 600mile trip and was only able to get between 12-13mpg. Mileage was great with the Stock Program and factory manifolds (16-17mpg) but as soon as i replaced the cracked manifolds with the set of LT Headers it went south.

-Habbi-

Yikes! I'm not an expert in any way regarding the effects of LT headers. My understanding is that they CAN provide modest power gains, but that there are so many compromises (to make them fit into the truck) that they may not deliver all that is promised. In addition, if you're still putting the exhaust into the "Y" pipe, you're probably defeating the whole purpose of them.

Cleatius12r (Cody) and 88Racing (and of course, Bill) are much more knowledgeable in this area though. They might have some ideas.

Your mileage sounds VERY low to me though. Was that computed at fillup (miles driven/gallons added) using a correct value for tire size? Putting larger tires on and not correcting for them would reduce the odometer reading at fillup.

With 33-inch tires and towing, I think I'd use 4.10 gears. My truck has 3.75 gears and 32" tires. I think it would be "kinder" on the driveline to use the higher gear ratio if you are towing 5,000 # or so. I suspect your gas mileage would be about the same with either 3.75 or 4.10 gears though. I wouldn't go higher than 4.10. Ford has a funny way of changing the max torque output downwards if the load sensed has dropped too much.

If you have 4WD, you're going to have to change the gearing on BOTH axles. This gets a bit expensive.

- Jack

[Habbi98]

Jack - my tire size is actually smaller then factory. Factory specs are 31.5 and the tires that were on it when I bought it are only 30.6 which is what really strikes me as strange, because you'd think it would have helped on the power end of things. I am hoping that I can actually get a hold of Bill this week sometime to see if he has my tune reworked so I can get it downloaded to see if it helps correct the mileage and power issue.