Ok, heres the problem. Ive got an 05 screw with the 5.4 and every time it gets to a mild to moderate hill in overdrive while doing about 70 on cruise control it downshifts. This is without pulling anything and no extra weight in the bed. Recently I added new 33 x 12.5 inch tires and obviously it made it worse. Now even on very small hills in cruise it will downshift.

In my experience downshifting with such regularity is usually bad for the transmission thats why you dont drive in overdrive when pulling anything. Do I need to just never use overdrive unless its completely flat or are the newer transmissions tough enough to take the repetitive shifting?

Is there anything I can about this? Powerchip...gears....whichever? Im assuming this is a very common problem.

 

Every vehicle that I have ever owned with an automatic overdrive transmission has done this. Cars, trucks, suvs, Fords, GM's and Jeeps that I have owned have all done this. The overdrive gear on most all vehicles are too high to pull the vehicle up a hill. Of course, installing taller tires makes this worse.

 

Part of my one way commute to the office is approx. 50 miles on two different highways, with the cruse set to 60 for the first half, and 70 for the second. My truck never leaves overdrive. This is with stock tires and 3.55 LS. I've actually mastered a "throttle feathering" technique where I can make it through an interchange without leaving OD (As long as no one is in my way ). Now I'm not climbing any mountains along the way, but this is in southwestern PA. There are a few moderate hills involved. My previous truck (Chevy Colorado) would constantly shift in and out of OD.

My guess is the tire diameter is causing the problems on yours. If you have 3.55, you could try 3.73 to offset the difference, although a 33" is not that far from stock. (My 255's are 31" tall.)

When you're crusing at 70, what RPM does it hold in OD? Mine sticks right at 1900. At 60, it's something like 1600-1700.

Check your tire pressure also. Running under-inflated can add stress to the driveline.

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Ive only had one other car that would do this and it was severely underpowered, something this truck is not. ^^Do you normally just never use overdrive?

RPMs at 70 is about what you said, just under 2000. Tires are inflated correctly.

Am I right that even with newer transmissions that constant shifting will overheat the tranny?

Im sure changing the gearing would help this but its not very cost effective on a 4 x 4. Would a superchip help since this supposidly changes the shift points.

 

i needs to down shift for a little extra torque to maintaine the speed you are going up the hill

 

At highway speeds without a load, I don't think there is any chance of overheating the tranny because of the shifting.

Did you notice this shifting with the stock tires? I'm leaning towards the larger rubber causing this.

I can't comment on the chip addition. I've never really messed with those before.

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this downshifting wont cause overheating of your tranny. Its normal operating shifts.

I just wouldnt worry about it.

 

^I kind of figured that considering there is no added load from pulling anything.

^^Truck did this before I changed the tires.

 

The larger tires changes the effective gear ratio in a direction not favorable to road speed ver engine power.
I have an 02 with a 4.6 and while it does down shift at a certain grade levels, it does pull in OD quite well for the truck and cruise design it is and weighting 5600 lbs.
My feeling is your bigger 5.4 3 valve should make more torque than mine and hang in there better than that (with stock size tires).
The throttle position and speed sensor togather with the ECU program control the shift points.
Some combinations hang in better than others.
You need to try and understand that at 70 mph and 2000 rpm or maybe less with bigger tires, there is not enough torque being made by the engine to keep nealy 6000 lbs going up hill at a stready rate without needing more power.
The only way that happens is down shifting to get the engine rpm up to make the power to pull the weight.
Can't get around it.
I have a 4000 lb Lincoln Mark VII with a K.B. blower, now that's a different situation.
The engine has the torque to run hills without down shifting out od OD.
The weight is lower, the torque is high so the hill and the weight means nothing to the engine.
These are two oppisite extemes to illistrate the differences.
There are other differences between the two but we can't change designs of the Cruise Control systems that are different between the two vehichles.
Bottom line is you have to look beyond just the simple operation that may not quite fit according to one's common level of thinking and take into consideration the physics behind it.
In my opinion, Cruise Cotrol in these heavey trucks operate poorly by vertue of the low torque the engines makes, weight of the truck etc. but does work, never the less.

 

BG - I payed close attention to it again this morning, (with this thread in mind), and once again, I travelled over 60 miles, with 1 interchange (between I-79 and Penn. Turnpike I-76), and not once did the truck ever leave overdrive. Not even on the on/off ramps! RPMs hold steady at 1600 or so at 60 MPH, then go to 1900 when I bump the speed up to 70 MPH. (Side note - Anyone else notice that if your crusing at say 60, and you want to go 70, all you have to do is tap the set/accel button 10 times? Same applies for the coast to lower speed. Each tap = 1 MPH. Pretty cool. )

Along the way, there are many considerable grades involved. Like I said before, no mountains, but a few hills that you would think would cause the truck to hop down a gear. This thing just hits the hill, and pulls without so much as loosing a single MPH.

I have no clue what I'm doing right, but this truck never ceases to amaze me daily.

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Ya got a good one there. I will try that ACCEL the next time I go out.
I'm loading up to go to Silver Spring speedway so not much use of cruise contol pulling the trailer, this time out..