'06 Sierra shifting hard/clunking on acceleration.

DallasEdition · April 16, 2014

I have a 06 GMC Sierra 1500 crew cab, currently 27,000 miles, 5.3, 4L60-E transmission, tow package,3.23 gears, and locking differential. My problem is when up-shifting from takeoff. When making a casual takeoff from a stoplight, shift point around 1400-1600 rpms, the transmission is smooth like butter. When making a little more spirited takeoff, shift point around 1900-2100 rpms, it feels like its slipping and jerks a little bit when it shifts...almost like it's catching up to slack in the driveline. It sounds like a quick, high pitched clunk, and I cant tell if its coming from the transmission or the differential. Fluid level is good and has a new, pink color on the dipstick. Its not been lifted or modified in any way. From what I can remember, it only does it after its had a chance to warm up.

Im not sure if this is related, but while driving with cruise control on the interstate everything is normal until going down a pretty steep hill. Its as if the transmission keeps pressure built up and wont let it completely coast down the hill, sometimes even bucking a little when going down the hill. Ive had a 10 Charger that would do the same thing and would actually down-shift to keep the same speed, and a 00 Silverado and a 04 Sierra that never did anything like this, so I dont know which one its supposed to do.

I bought this truck in Jan. 14 with only 24,000 miles on it. From what I was told the truck had the miles put on it and then sat for a few years, until I bought it. Sorry for being long winded, but I wanted to give as much useful information as I could possibly think of. Any ideas?

lilAL87 · April 29, 2014

my 2003 2wd shifts the same way but i have this whinning noise also not sure if its the trans or the engine but it def. shifts the way your truck does if you figure it out please let me know as i will do the same

00Silverado4x4 · April 29, 2014

An 06 with only 27k miles....wow. I've just rolled over 120k, anyway back on topic.

Your trans seems to react opposite of mine, when I drive like a grandpa I get the clunks and what not but with spirited driving she will go through the gears like butter. I've gotten under the truck and noted there is a little bit of give on the driveline components. It's always been there and never gotten worse. I know you have so few of miles but since it is an 06 I'd have all the fluids changed out just because of age. Then put some mileage on it and see how it reacts when driven. Could be just old fluids that need to be retired. Every GM truck I've ever owned/driven always had clunks and what not in the driveline, but then I've never had one give me any serious grief unlike the wife's Jeep. Driveline is silky smooth in shifting and driving but then the trans has developed 4 leaks, rear pinion seal leak, broken wires in the driver's door hinge area, blah, blah and blah some more.....