First off, my truck is a 2009 with a 5.4L, 3:73 gears, 6"lift, and 35x12.5x20 Toyo MT's on it. Here is what I have noticed on the past few road trips that I have taken;

If I set the cruise control and remove my foot from the accelerator pedal it will downshift on a hill of any size. It generally downshifts directly to 4th anytime it downshifts and then comes back to 6th after the hill.

However, if I set the cruise and apply just a little force to the pedal, it will pull like a champ without downshifting. By applying a little force to the pedal, I mean generally somewhere around 10 - 15% according to my EDGE CTS. Then if it does downshift it will only drop one gear and not two. Sometimes as little as 5% of the pedal is all that is required, but it must be applied ahead of the hill or increase in load. It is never enough to pickup any speed before the hill, but just show up on my CTS.

I wish there was a way to get the truck to act like it does when my foot is on the pedal all the time. Anybody else notice or tried this?

 

you try the tow haul button before the hill

 

Yep, similar results in Tow/Haul. These are hills as small as overpasses that occasionally cause the truck to shift so I'm not talking big hills.

Sounds like I can get some relief by working on my custom tune some more.

 

its probably due to the bigger tires. before i put the 33" BFG's on mine it was very reluctant to downshift. if im using cruise control i just give it a little gas before the incline and it does just fine. just cut cruise off if theres one after another.

 

Cruise is reactive not proactive.

 

I have updated my symptoms to state that my truck often shifts directly to 4th anytime it downshifts while using the cruise. If I apply just a little pedal, it will pull the same hills in 6th. Sounds like I need to give Bill at PHP a call and have him tweak my tune a little.

 

Factory tune does the same thing.

Essentially in cruise: you hit the base of the hill, vehicle decelerates a couple MPHs, the computer senses that you've slowed down, and it will down shift to accelerate back to set speed. But unfortunately you're headed up hill by this time, so it really has to down shift and wind up the RPMs to get back to speed while going up hill. The system is reactive based on what has already happened to the vehicle.

If you see the hill coming, and you can over ride the CC by slightly accelerating at the base of the hill, the truck can maintain the speed just needs help with the transitional phase as it "learns" the grade of the hill in terms of engine load. By helping the system ahead of time you are being proactive

 

Well said! I was trying to think of a way to explain it, but Patman's answer is excellent!

 

Thanks

 

I noticed this too, long ago. It is too bad that my foot can get better gas mileage than a computer can.

 

Mine is the same way, same size tires, same gears.I have vmp tunes on my sct and have made multiple attempts too get this fixed and Justin ignores my emails now.he did make 2 revisions on my tunes but just made it worse.I wish I could get a tune that would fix it as well.I am very disappointed with my $500 Speedo calibrator and the customer service I received from him, so if anyone gets a fix I'd love to hear as well. I mean it's awful how bad it affects the mpg in cruise.