I'm at around 156,000 miles on my 14 Sierra. Purchased new in Oct 2013. Truck has been good overall. Has never left me stranded and only once didn't start (weak battery which I replaced this winter). I try to stay on top of maintenance. Here is an overview of what I have done:
- Change engine oil/filter every 7300-7500 miles. Basically following the OLM to 5% or so. Been using Mobil 1 except for the first few complimentary dealer changes.
- Changed transmission fluid by doing drain/fills through the dipstick. Can get about a gallon out each time. Would do this 3-4 times (drive each time between exchange). First time was around 60,000 miles followed again about every 30,000 miles. Dropped pad and did filter a little over 100k.
- Air filter every 40-50k. I don't drive in very dusty conditions and they have typically looked OK.
- Cabin filter once year
- Rear differential fluid around 50k and again around 140k
- Front differential and T-case around 80k. Will probably do again at next engine oil change.
- Spark plugs and wires around 100k. They actually looked good and probably could have gone further.
- Dropped lower radiator hose and emptied overflow bottle last fall (150k miles) and replaced with fresh antifreeze.
- Replaced all engine belts (primary serpentine, vacuum, and AC) last fall the same time I did the antifreeze. They didn't look terrible but were certainly showing wear. I had developed a slight 'tick' coming from the front of the engine. New belts seems to have solved that problem. May have been a little rock or something but I figured after 150k they were due regardless.
- On third set of tires. OEM till around 50k then Cooper Discover ATW till around 100k, then Falken AT3W which I'm still on. They have been wearing good and still have at least 10k in them.
- Still on original brake pads and rotors. May replace them (and fluid) sometime this year.
- Front drive door was noisy while driving with a cross wind. Had dealer adjust and problem went away (under warranty)
- A few computer updates
- Loose driver seat. Would feel like it would slide left/right when turning. Fixed under warranty with kit GM released.
- One of the rear shocks began to squeak. Removed and it appeared to be leaking and didn't feel right. Truck was still under warranty but I replaced myself with Bilstein 4600 series which were a little better overall. Also later replaced front shocks with Bilstein 5100 series on 2nd highest level. Front shocks were still good so this was more for looks.
- Did replace the vacuum pump as preventive maintenance item (even though it's technically not a maintenance part per the manual). I had suspicion my pump might be on its way out due to a noise I could hear coming from that area. Not long after I replaced it, GM issued the bulletin regarding replacing it if you had braking issues. I never did have brake issues but was more concerned about it "grenading' and sending debris in the engine oil.
- Have a vibration around 75-80 MPH. It's not violent but noticeable. The strange thing is I don't recall having it when the truck was new. Not sure when it really developed.
- Had a rattle coming from the passenger front door. Took the armrest off and made a little shim between it and the door where it seemed to be rubbing. Seemed to have fixed the problem.
- The torque management, numb throttle, poor transmission programming, and V4 makes for less then exciting driving experience. Transmission is way to eager to get into the next gear and the throttle requires a lot of movement to make power. I bought a Diablo inTune i2 tuner around 90k and installed their 87 octane tune and added throttle boost. Also did the firm transmission tune. This helped some (held gears a little longer) and make it a little more responsive. Also disabled V4 mode which I didn't think helped much anyways. Wouldn't stay in V4 mode long unless I was driving 55 MPH (which isn't often).
- Factory headlights were pretty poor. Added an HID kit.
- Coating on frame started coming off within the first year or two. A lot of surface rust on the frame now. I've just accepted it.
- Paint on front bumper (AT package) is thin or just plain poorly applied. It's covered in 100's of little chips. Wish I would have it wrapped with that clear film. What's interesting is the paint just above the bumper (grill and headlight surrounds) isn't near as bad. Just seems like the bumper has poor paint.
- Developed a stain on the headliner. Appears to have come from the 3rd brake light as the bulb was out. Suspect water got in and stained the headliner and burnt out the bulb.
- Something inside the tailgate latch broke when trying to open the tailgate. Partially my fault as the tailgate was a little stuck (cold weather makes it stick to my seal kit and tonneau cover). Replaced handle myself (pretty easy fix). Can tell new replacement handle is designed a little differently so there must have been a design change at some point. Thought the original looked a little weak.
Overall I can't complain too much about the truck. No rust on the body that I'm aware of and the paint (except the bumper) is good overall. Most of my issues/dislikes appear to be somewhat common. I don't drive the truck as much as I used. Was averaging at least 25k a year for the first 4-5 years. Started a new job in Sept 18 which provided me a work car which is now my daily driver. Sierra gets used on the weekends and mainly to pull the boat. Still runs strong and doesn't burn much oil (maybe 1/2 quart every 4000 miles or so). Since I don't drive it that much, I really haven't gotten too serious about trading it for something different/newer. It's paid for and plan to keep it for at least another couple years. Will wait and see what GM does with the 2021 models.