Unspooling

If you are driving with the cruise control on and start to go up a hill, your vehicle will shift and accelerate to go up the incline. Call it "spooling" up power or energy. My 2003 (Vader) will, on some inclines, not all, "unspool". That's the best way I can describe it. It only happens when the cruise is engaged. Tap the brakes, disengage the cruise and everything works fine. Usually. Sometimes it seems to hang in this state and you cant accelerate from a dead stop. Its becoming a problem because its happening more and more often. Any ideas? How do i fix this?

More info would be helpful such as how many miles on your AV? Have you had any drive-train work on it lately? How about any electrical work?

what you describe is DOWNSHIFTS and accelerates.

It does not have to downshift all the time on cruise if it can maintain the speed or only lose a few mph  it will not downshift.
It will just struggle up until speed drops off too much then it should downshift and speed up faster

230,000 miles. No drivetrain work recently. No electrical work either.

Ygmn, it will struggle (or at least start to) for a minute and when it should downshift it changes gear, revs uncontrollably and loses speed like it's in neutral. This is the problem.

Sounds like it is time for a tranny rebuild or replacement.

This problem only occurs when the cruise is on. I'm wondering now if there is a "cruise control" module that could be acting up. I cant find any trouble codes that could be tied to this issue. Some one asked if I could have the wrong MAS installed? Previous owner really did a number on this truck, so anything is possible.

The PCM has transmission parameters set for Normal, Tow/Haul, Cruise, and Hot conditions.  I don't know why one would set it up to operate as you have described in Cruise Control mode but it is possible that a tuner has done that I suppose.  On the other hand previous owner may have tightened some things up in Normal mode to hide the fact that the tranny was on its last leg.

Where is the PCM? How do access it? How do I change settings?

Oxcart said:

Where is the PCM? How do access it? How do I change settings?

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PCM is pretty much below the battery, a bit towards the rear of the truck.  Look for where a couple of cable sets are going.  It is protected by a piece of plastic (of course  .

Once you know where it is it isn't that hard to figure out how to access it.

As far as changing settings, you can do that through the OBD II interface inside the cab, although you either need to be a computer wiz kid or purchase something like HPTuners' interface and software with a laptop.  I'm a professional tuner as well as an authorized HPTuners dealer.  You will need one of their interfaces, $299.99, to read out your tune and view it on a laptop.  You will need to buy 2 credits at $49.99 each for you to make changes to the tune and load into your truck.  These are the HPTuners list prices - my reseller agreement doesn't allow me to discount their prices.  (See www.hptuners.com).  That said, I do have a license for all 2003 Avalanches and if someone buys an interface through me I can remote program through their interface and save that person the $100 for the credits.  I currently have a new interface in stock but with 8 credits - it would cost about $700, but I can place an order for you for one without any credits and have it drop shipped to you.  Once you receive it I can walk you through it, help you pull out the current tune, have you email it to me, I'll then look it over, and if there's something that needs to be changed can change it and then email it back to you.  You can always add credits later if you want to take the wheel so to speak.

Didn't mean to make this a sales pitch but since you asked...