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Old 06-03-2009, 07:00 PM   #1
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441 miles, and 11 1/2 hours ago, I left Concord, went to Richmond to pick up the cargo, stopped off in Fairfield and picked up blood and delivered that to Woodland and then proceeded to Reno to deliver the Richmond load.

Bay Area to Reno, where I gassed up, 19.3 MPG. Goody.

Now to shifting.

I know, It's a Tundra, but the Dakota did it too, and I bet so does every other automatic, and I am curious as to why this happens;

The transmission shifts back and forth, going up hill, while on cruise.
Take it off cruise and hold exactly the same speed and it doesn't shift out of the same high gear it will not hold in cruise.


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06 4.7 Tundra replaced a 98 Dakota 3.9.
623,000 miles on original engine and transmission, using Amsoil by-pass filters and lubrication.
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Old 06-03-2009, 07:35 PM   #2
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My guess is that the cruise control is changing the throttle position more abruptly than your foot does and thus the transmission controller "sees" the lower engine vacuum and downshifts as it is programmed to.

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Old 06-04-2009, 04:52 AM   #3
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Everybody says that cruise is not smooth or changes throttle abruptly; I have never experienced it. It has always been a very smooth, slow adjustment. The only difference I've experienced is that cruise will keep adjusting when a foot might quit and allow speed to drop. I've mostly used cruise in GMs and my VW, if that makes a difference.

I'm pretty sure that modern transmissions don't bother with vacuum at all, the computer reads TPS and RPM.
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Old 06-04-2009, 05:19 AM   #4
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The only time my V10 wants to downshift on a hill is when the air filter needs replaced.
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Old 06-04-2009, 07:18 AM   #5
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It's in the cruise algorithm. They routinely take the transmission out of overdrive way before just pressing the throttle would because by the time it gets to that point it needs to accelerate about 3-4 mph to get back to where it was set so it downshifts to do that earlier. The Durango will do it at high speeds so I just hit the overdrive button and keep it in 3rd until the end of the hill.

I've been in cars that will downshift and then accelerate when you resume from a lower speed back to what you were at. It's a weird feeling!
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Old 06-04-2009, 11:52 AM   #6
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The last speeding ticket I got was the week Princess Diana died. It was in a 97 Altima and I was using cruise control. Not enough engine braking downhill.
The infamous Emporia Virginia speedtrap, cop at the bottom of the hill. Cruise allowed the car to go 69 in a 55 from a 62 setting.

I will not own a car with cruise control after tomorrow when the Mercedes will be sold.


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