O5 LLY.......Cruise works fine...Just seems to be slightly on off gas on flat ground.......Normal?

The dead band for the cruise control circuit is wider with an Allison due to GM wanting to minimize "shift busyness" as they call it when towing.

The end result is that you see a little more speed changes to prevent excessive downshifts and upshifts.

my 04.5 LLY hunts quite abit as well. And it will overshoot the mph at the top of a hill by 3 or 4 mph, then go under the set speed, then back over a little bit, then finally settle in. It's actually quite annoying, my LB7 never did that. Not only is it a pain, but it does cost some fuel mileage. I continously run the same 300 mile stretch, I did a little test vs. cruise and no cruise over several runs. My foot manages about .3mpg better than the cruise does. -:tSo much for the wonder of electronic throttle control.:rolleyes:

Pwdr Extreme, mine does the same and it is a result of the speedometer calibration being off from the stock tires to the LT265 Revo's I have on now. Mine is off like 4%.

The control algorithm used to control the cruise setting is off because of the speed input. For example; when you ask for 1mph faster, one push on the accel button, it takes that 1mph faster and gives you 1.04mph, then the algorithm sees that it got more then it asked for and then backs off to compensate. Because the algorithm is really quite crude, it compensates too much and you get a trend of over and undercompensation until it gets within tolerance of the speed you asked for. Same thing happens when you approach an incline or decline.

So the only way to fix this cruise problem is to recal the speedo for the tires you are running.

Hope that helps you understand it.

Grabs I'm sorry to say it but that is simply not the reason why. The truck has no idea what size your tires are because it has nothing to reference it to.

I'm running the tires the rig came with, so that shoots down that theory. Plus it has done it from the day I bought it brand new, so it does it stock as well as "modded". I dunno what the differenc is, but my LB7 always worked great, even modified. Plus all my other dozens of GM rigs all work right.

Your performance mods will not help anything. Does it do it completely stock?

Yeah, my basically stock performance-wise LLY does the same thing with 245's. It's kinda annoying, but it sounds like this is the norm on the LLY's. I attribute it to all those horses under the hood wanting to cause a "runaway"!

My cruise seems to run just fine unless I set it really low like 45 or something where the rpm is getting down where there is less torque. Then it makes it go up and down a little bit. Still not that bad though. At higher speeds 60+ it never has any problems staying even on the hills.

I have the same problem and I'm rather annoyed by it. Some hills are worse than others where it will exceed the set speed (by 2-3 mph) then coast (to 2-3 below) then hard acceleration back up again all before that top of the hill. It will also do it on flat ground especially when pushing into the wind. I had an 02 gasser with the allison before this truck and it would hold the speed within a mile in either direction of the set speed (unless towing). I asked the dealer about it thinking it may be a faulty speed sensor or something, the answer "normal, nothing can be done about it".

Could it be lag associated with boost, or possibly the EGR wait for the valve to close?

The more power you add to your truck, the more it will hunt when cruise is set.

I had computer, intake, and exhaust upgraded on my 02 with the 8.1 Allison. Also had the same size tires (265's) on the last truck as I have on this one. The cruise worked perfectly on that truck, but this 2004 duramax is just annoying.