I been having this problem with my truck since i bought it(used). Its an '03 Silverado E/C 4x4 with the 4.8L, and 65,000 miles.The problem is, when i am going real slow, or coasting, like if i'm coming into a hill and i have to slow up, due to we'll say a horse and rider, or a kid on a bicycle.I slow up, as not to startle the horse. Well, when i go to accelerate, once i'm past the horse and rider, the truck is down shifting, and when it does, the rearend clunks pretty good. I also notice 1st thing in the mornings when i take off with my truck, (we live in a trailer park), the speed limit is 10 MPH, butthe truck seems to stay in 1st gear longer than i think it should. Could the tranny be not shifting correctly between 1st and 2nd, and 2nd down to 1st? The RPM's drop to around 650 - 700, but i believe it was you that said it sounds like the tranny is trying to take off in 2nd gear, and when it down shifts to 1st, the RPM's are too high andits clunking. And just before it does this, i can tell everytime as the throttle response is very mushy. Heres what i have done. I changed the fuel filter, and last weekend i cleaned the throttle body, by spraying carb & choke cleaner into it as it idled til it stalled the motor. I was wondering if all this could be caused by a dirty transmission filter? There are NO CODES, NO CHECK ENGINE LIGHT, and my dealer has put the truck on the OBD2, and nothing. When i cleaned the throttle body, i thought it fixed the problem, as it ran 100% better, as the RPM's stayed @ about 1,000 RPM's, until i almost came to a complete stop, then they would drop to 650 - 700.Throttle response was right there too, for about a day, now its right back to square 1. As this is such a long and in depth post, if anyone wants to respond directly to my email address, its mymissionisfishin@msn.com . PS, I am actually leaning towards, it having to do with a dirty tranny filter, not allowing the tranny to shift correctly. Let me know what you think, Thanx, Jim

 

Is there a throttle cable or are those fly-by-wire?

 

FLY BY WIRE, ALL ELECTRONICALLY CONTROLLED.

 

I still think this truck MAY be taking off in second...if that is true,there is a bulltin from gm about it.It has us "reflash" the pcm with a software upgrade.Your dealer should always check for upgrades when chasing something like this...something that may well be a software issue and not a hard part failure.

If the tranny filter were plugged,you'fd get stuck in 1st gear...for a long time,every time.

another good possibility is the shift solenoids...indside the pan...they are terrible to diagnose,andyou pretty much just have to go for it.If you remove the pan to change the filter..change those 2 solenoids while your in there.
I still would like to see it updated though...ask your dealer about it...should cost you about 1 hours labor

 

Update: I checked with a tranny place and they told me, basically, its from when the rearend has pressure on it, to when it down shifts, the pressure is released, and when it grabs another gear, thats the clunking noise. Not sure if that makes sense to you but it did to me. . My dealer checked, i have all the newest updated software. So, i guess i change my style of driving, and will have to ease into the gas until the RPM's are higher, then i'll be all set. The wifes Avy has the same tranny, cept hers is an '02, and the 5.3L, but her truck does not do it. Dealer has no reason why?

 

Yanno...There was a bulletin about changing the transfer case fluid to a new blue fluid...to fix a stick condition of the yoke getting stuck in there....

 

Mine has made a clunking noise when i come to a stop and then take off not fully stoped i think it is the yoke? Right argon is there not something out there like this and the dealer does something but i forgot what they do.

 

if its 2wd,remove the driveshaft and put some waterproof lube in the yoke....4wd,do the mentioned fluid swap