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Old 07-21-2018, 11:37 PM   #1
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Towing question - cannot maintain speed on steep grades

I have a 1999 GMC Suburban K1500 which has a towing capacity of 6000-7000 lbs and a 1999 Jayco Heritage popup (approx 3200 lbs I think). On flat roads towing is no problem, but in the mountains, going up steeper grades, I am lucky to be able to maintian 45 MPH running at higher rpms. What concerns me is other 1/2 ton trucks pulling heavier campers/trailers pass me like I am standing still.

Any ideas? Thanks.

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Old 07-22-2018, 12:14 AM   #2
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I doubt a 1999 vehicle is running a peak efficiency and power so while it may have been rated to tow 6000 lbs when new may very well struggle after 19 years of usage. Also, the power and towing capacity of 1/2 ton trucks has greatly improved over the last 20 years. There is really no comparing newer 1/2 tons to the trucks made even 10 years ago.
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Old 07-22-2018, 12:18 AM   #3
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I doubt a 1999 vehicle is running a peak efficiency and power so while it may have been rated to tow 6000 lbs when new may very well struggle after 19 years of usage. Also, the power and towing capacity of 1/2 ton trucks has greatly improved over the last 20 years. There is really no comparing newer 1/2 tons to the trucks made even 10 years ago.
Thanks @2edgesword. I should have mentioned the engine was replaced and has 15k miles, the transmission is original as far as I know (160k miles).
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Old 07-22-2018, 12:39 AM   #4
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Your engine, axle ratio, payload etc. all play roles in tow performance. Your vehicle, 4x4, weighs approx. 6000lbs empty and the gas engine that year had 255hp which is 100hp less than current models. You should know your loaded weight for your vehicle when fully loaded and the weight of the trailer when fully loaded. Answers to these questions will help you narrow down the problem.
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Old 08-29-2018, 09:11 PM   #5
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Towing in the mountains is a whole different animal when compared to flat and/or sea level. You can easily subtract 10% from your towing capacity when towing at elevation especially if you don’t have a turbo. The air is much thinner when you get above 7000’ and combustion sufferers which of course is where your power comes from. Most Flatlanders never consider elevation when giving advice about towing capacities or suggesting a tow rig.

Start with a high quality air filter NOT a K&N!!!!!!! This will help the engine breathe when going up mountain passes. Use your Tow/Haul button if you have one OR down shift manually and just slow down. You’re basically taking your transmission out of OD, this will allow higher rpms to maintain your speed. If you have to just get in the right lane and turn your flashers on , truckers do it all the time.
Go to car wash and gently rinse out the radiator, transmission cooler, and ac condenser. Although not a power fix it’ll save your diff, flush your rear diff and replace with heavy duty diff fluid (85/140) If you have LS check to see if. You need Friction modifier. If you remove the cover buy a Lubelocker gasket, they’re cleaner and reusable instead of using RTV sealant. Good luck.
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Old 09-06-2018, 07:58 PM   #6
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why not a K and N? is there a better filter brand to use?
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Old 09-07-2018, 09:17 PM   #7
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why not a K and N? is there a better filter brand to use?
K&N are known to flow more air BECAUSE they filter less. AFE makes a good filter (stick with dry). Id run a stock filter before Id ever run a K&N.
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Old 09-07-2018, 10:13 PM   #8
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The gear ratio of the vehicle has the greatest effect on towing up and down grades. A 4.10 rear will out pull a 3.08 ratio and so on. Turbo diesels will make a gas engine look like they're standing still. Check your gear ratio and I bet that's the issue.
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Old 09-08-2018, 10:01 AM   #9
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The gear ratio of the vehicle has the greatest effect on towing up and down grades. A 4.10 rear will out pull a 3.08 ratio and so on. Turbo diesels will make a gas engine look like they're standing still. Check your gear ratio and I bet that's the issue.
I agree on the gear ratio, in the mountains that is a big factor.

As for Turbo-diesels will make a gas engine look like they are standing still... That may hold true for the basic gas engine... the EcoBoost with the twin turbos.. well we passed the diesels going up the 7% grades like they were standing still, cruise control engaged, going 60mph. One of the diesel owners got the spot next to us in the camp ground and said he was amazed at how we by, he said he was in line behind a few other diesels. Also said he was going to head to the FORD dealer and look into an EcoBoost. Got to love them!

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Old 09-13-2018, 08:55 PM   #10
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As for Turbo-diesels will make a gas engine look like they are standing still... That may hold true for the basic gas engine... the EcoBoost with the twin turbos.. well we passed the diesels going up the 7% grades like they were standing still, cruise control engaged, going 60mph. One of the diesel owners got the spot next to us in the camp ground and said he was amazed at how we by, he said he was in line behind a few other diesels. Also said he was going to head to the FORD dealer and look into an EcoBoost. Got to love them!
Not to start a flame war, that's likely because the turbo diesel guys were pulling heavier rigs or had trucks that were 5+ years old. I used to think the same thing when passing others towing my Salem. I've had both the EcoBoost and 6.7PSD (current), no way I would go back. Not nearly as much downshifting, better MPG, and my truck doesn't sound like a weed whacker pulling 5k going up a steep hill. Both do the job however.
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