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It feels exactly like a tire is out of balance, except that it's something mechanical. I swear it's gotta be pretty common, I'm starting to think there's a lot of people out there that don't even realize it or aren't picky/don't care that there's a vibration.

Well there is hope boys! Just got my 14 Sierra Crew SLT back yesterday and I'm tentatively calling it fixed (95% sure, have to drive it more to be sure). It had a vibration only in the steering from 65-75kph originally. First service they replaced 2 tires and returned it with a worse vibe. 2nd service they replaced another tire and returned it slightly improved but not as good as it was originally. 3rd service they replaced the drive shaft, returned it with a dramatically worse vibration 60-80kph, that could be felt in the whole truck and a slight vibe at nearly all speeds. So then I went in and ranted at the service manager for 20 minutes about a week after 3rd visit. He booked it in for the next day, then the service level improved quite a bit. Had a loaner waiting for me. They had it for 11 days (due to waiting for parts) and replaced the rear diff gear case, crown and pinion gears and bearings. I believe they also rebalanced the drive shaft or possibly put the old original one back on. Boom, they got it, after I had lost all faith in them they turned around and redeemed themselves. I don't know if I'll ever think highly of GM again though, that's kind of ruined for me. Also had them apply the headlight upgrade while it was in, it's a noticeable improvement I'd say. So now after 2 months of dicking around with that I think I'm a happy camper, fingers crossed. Truck has 3800km on it now, was built and purchased in Sept/14.

Thanks for those links, they provide a lot of insight into what is needed to fix the vibration problems. Just to get all the info centralized, I've gathered the following TSB, worksheet etc. info to show the service departments in case they're unable to find their ass with both hands on this issue: GM TSB PI1354B Vibration Analysis Worksheet – Bulletin 03-00-91-001G CH-51450 Oscilloscope Diagnostic Kit with NVH I found a link to the actual worksheet PDF if you click it.

Thanks, that will probably help. I think on mine I gotta find out what went on with that replacement tire that wouldn't balance and they possibly threw it on the truck anyways to see if it was good enough. Hope not, that would be a bad way to start things off.

Nope, no difference between V4 or V8 mode for my vibe. It is different depending on how hard I accelerate or decelerate through it. I had a 2007 Avy, so I've already had my fun with first gen AFM issues like mysteriously burning a quart of oil on a 2hr trip randomly once or twice a year.

Thanks. Would you be able to send me or post the tsb so I can take a look at it?

Sadly, I have to add my truck to the long list of ones with vibration issues. Bought in Sept 2014, 2014 Sierra CC SLT Z71 4x4, has 2200km on it. It's had a bit of a vibration from 65-75kph, strongest at 70kph since new only in the steering wheel, definitely couldn't feel it in the peddles or body or anywhere else. So it wasn't too annoying and I honestly think it's the wheels/tires, so finally last week took it in and described the issue and me and service agent agreed it seemed like a balance issue. Dropped off 8am, said they had a busy day, by mid afternoon said they need to keep it over night because they ordered 2 new tires because both on the right side would not balance in spec. So they keep it until the next day, get a call in the afternoon that the new tires are installed and balanced but... still a slight vibration from 70-75kph. He said they can keep it and keep checking the driveline for a bad ujoint, driveshaft etc. or I can come take it for now and see how it is. If I don't like it they can proceed with more work next week. So I pick it up and sure enough it's like the vibration has been narrowed down to more like 70-77kph. I wouldn't necessarily call it less of a vibration, just different, like a bit higher frequency, and actually slightly more annoying than the previous initial vibration that was over a wider speed but slower frequency, and I swear there's a hint of it in the gas peddle now where as there was none before. Anyhow, that's a bummer, and I swear after reading on here I'm still maybe gonna push going another round on the tires and wheels. Because they definitely changed the vibration with 2 days of adjusting and 2 new tires. I'm weary of going down the long road of tearing apart the driveline on my brand new truck. But check out the work order and tell me if it looks like the second of the 2 new tires they got was also a dud with an initial road force balance of 32 lbs and then machine said couldn't balance... then what? the guy said F it and threw it on anyways? Here's the w/o: