High speed question
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Elder User
Joined: Feb 2011
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From: K.C. MO
High speed question
Had a chance this weekend to do a couple hundred mile trip across Kansas on I-70 and made some observations when traveling at higher speeds.
1. The posted speed limit is 75mph so the "real" limit is around 82 or so where you are actually in danger of getting a ticket so depending on traffic I was driving about 80. I noticed that if you are over 80 the transmission will downshift to 5 when you are going down small hills and upshift back to 6 when going uphill or slightly accellerating. This is counter intuitive to me and gets kind of annoying. Set the cruise for >81 and it will constantly shift back and forth between 5 & 6. Set it for 79 and it does not do this.
Anyone else ever notice this? Yes, I did have the NOX recall refllash a week or two ago.
2. Some of the turnpike expansion joints get the porposing effect going so bad it makes you want to pull over and stop after a while just to rest.
Other sections of road that look identical are smooth as glass. 
3. Milage drops about 2 MPG from the average at these sustained speeds. I would have actually expected a little worse.
This was all in an unloaded truck, very little wind, hot (around 100) so AC on and with a tonneau cover.
1. The posted speed limit is 75mph so the "real" limit is around 82 or so where you are actually in danger of getting a ticket so depending on traffic I was driving about 80. I noticed that if you are over 80 the transmission will downshift to 5 when you are going down small hills and upshift back to 6 when going uphill or slightly accellerating. This is counter intuitive to me and gets kind of annoying. Set the cruise for >81 and it will constantly shift back and forth between 5 & 6. Set it for 79 and it does not do this.
Anyone else ever notice this? Yes, I did have the NOX recall refllash a week or two ago.2. Some of the turnpike expansion joints get the porposing effect going so bad it makes you want to pull over and stop after a while just to rest.
Other sections of road that look identical are smooth as glass. 3. Milage drops about 2 MPG from the average at these sustained speeds. I would have actually expected a little worse.
This was all in an unloaded truck, very little wind, hot (around 100) so AC on and with a tonneau cover.
Post Fiend
Joined: Jan 2009
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From: Greenwood, SC
Cruise will downshift to keep you from gaining more than 2-4 mph on a downhill slope.
Going 80 requires a lot of HP. may be shifting to 5 to keep speeds going uphill.
I don't get why folks don't use M mode more often.......
Going 80 requires a lot of HP. may be shifting to 5 to keep speeds going uphill.
I don't get why folks don't use M mode more often.......
Junior User
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[quote=PITS;11990836]
2. Some of the turnpike expansion joints get the porposing effect going so bad it makes you want to pull over and stop after a while just to rest. Other sections of road that look identical are smooth as glass.
quote]
had the same experience this weekend - at or over 80, the truck (which was empty other than me) started to porpose and vibrate - drive it a few mph lower, it disappeared
2. Some of the turnpike expansion joints get the porposing effect going so bad it makes you want to pull over and stop after a while just to rest.
Other sections of road that look identical are smooth as glass. quote]
had the same experience this weekend - at or over 80, the truck (which was empty other than me) started to porpose and vibrate - drive it a few mph lower, it disappeared
Post Fiend
Joined: Oct 2002
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I'm with ruschejj - put in in M6 and let the torque handle it !
it will still downshift if it really needs to, but MUCH less often than when in drive.
on anything less than 3% grades it would hold speed even with the 5er chasing us.
Posting Guru
Joined: Nov 2010
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From: Altoona, Ia
Mine doesn't downshift when the cruise is set. I drive it in auto, I don't care for the Manual mode. I've had my truck as high as 90 and it doesn't downshift. Maybe H&S fixed that problem too.
Junior User
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Andrew, setting aside the downshift issue for a moment, do you get vibration/porpoising at the very high speeds?
Posting Guru
Joined: Nov 2010
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From: Altoona, Ia
No real vibrations as long as you're on good roads. Older stretches of interstate that have bad grooves worn in will give a slight vibration on occasion, but 99% of time there's none.
No porpoising either. She rides nice and stable no matter the speed.
No porpoising either. She rides nice and stable no matter the speed.
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Elder User
Joined: Feb 2011
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From: K.C. MO
From what I have read, the porposing is more of a problem with the long beds.
And yes, I found that M is better than D at speeds over 80. That is the magic number...80
As far as it anticipating "hills"...this is KANSAS we are talking about...Hill is more of a misnomer.
And yes, I found that M is better than D at speeds over 80. That is the magic number...80
As far as it anticipating "hills"...this is KANSAS we are talking about...Hill is more of a misnomer.
Laughing Gas
Joined: May 2008
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From: Central Kansas
But yeah...the girls in your sig pic have bigger "hills" than Kansas does.
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yes, i have a long bed...so that makes sense
Post Fiend
Joined: Oct 2002
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+150 hp will certainly allow your truck to pull more hills without downshifting than my stock truck - and I HATE you for that
writing assignment...
write "I will stay stock" 100 times on the blackboard
Posting Guru
Joined: Nov 2010
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From: Altoona, Ia
The op posted his truck was downshifting going DOWN the hill not up. Mine doesn't downshift up or down.
150 extra hp and 400 something more ft lbs is a pretty good time, I can't lie.
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From: K.C. MO
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