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113,****** miles on my truck. Transmission shifts okay. Had the GM service update done with Mobil fluid at about 30,000 miles. Looking to do a pan and filter fluid change this fall and considering some upgrades. Has anyone else done things such as a shift kit, deeper pan, or the transmission cooler bypass valve? What did you do? Which brands did you use?

Hey guys, I did the thermal bypass conversion to active by pass on my 2018 8L90. Did a step by step video because I hadn’t seen anybody do an actual full replacement video nor had I seen one on a 8 speed. Trans runs about 45 degrees cooler now. Check it out and let me know what you think. It’s the exact same procedure on 6 speeds just mounts different on the transmission.

My 2019 Sierra with 12,00 miles under warranty was diagnosed by the dealership. Was told the valve body need replacement that was 7 days ago now I’m being told a replace valve body is not available and they don’t have an eta for the part. Primary issue is the torque converter clutch disengages every 5-10 seconds at highway speed, in town it is much worse. Secondary problem torque converter clutch disengages the vehicle shimmies also at low speeds has a harsh shift.

Not sure if this has made rounds on this forum yet, but it was brought to my attention at work as we have a 2016 5.3/A8 in for this concern right now (we've done them in the past but its been a month or two). I've highlighted in red the big change, GM is no longer replacing converters based on their findings on returned warranty units as it can still come right back. The triple flush has been dropped for now, just a flush and re-evaluate. It does appear they must be on to something that is a better fix as they are working on one to be released Q1 2019. Looks like they will continue to only flush/fill them for now. This does apply to ALL 8 speed applications, both 8L45 and 8L90, EXCLUDING the new T1 1500 trucks. Stay tuned...

First post, been a lurker for 3 yrs...2017 High Country w/ 101K. Lost 6,7,8, gears and truck wont shift past 5th at all. Similar symptoms to others, hard hesitation then super high RPMs (low gear limp mode). Dealer inspects and says fluid is so gummed up the valve body, solenoids and some other sh*t is "stuck" and there is metal everywhere. Yep, had the torque converter issue at 30K, with dealer flush. $5K for a new trans with a better warranty than the stock, 3yr/100K...wtf. Apparently any "updates" GM has made will be in this shiny turd of a sh*t show. Anyway...after this disaster, I'm in prevention mode...new fluid after the first 10K, then every 20k (trans, diffs, transfer). Oil every 5k, this 8L90 sucks azz.

I have a 2017 Chevy Silverado 4x4 5.3l V8 with the 8 speed transmission. I already flushed out my transmission and filled it back up with the Mobil 1™ Synthetic LV ATF HP blue label. The question is, do i also use the HP fluid for my transfer case? Or do i need to use just a standard ATF fluid instead. I cant seem to find a straight answer on this. The owners manual states to use DEXRON®-VI Automatic Transmission Fluid. Would using regular ATF in the transfer case and HP ATF in the transmission cause any issues? Thanks in advance!

Earlier in the week my check engine light came on and I saw the P0700 and P0711 which lead me to Transmission Fluid Sensor issues and people having to replace them. I started monitoring the sensor and noticed it didn't fail like most other people but it takes an awful long time to warm up only peaking at 150F whereas previously it seemed to always be near 200. It took about 45 minutes of driving to get into the 140's and only passed 150F after another hour of driving after that. As I learned the thermostat is only supposed to open up at 192F so I believe mine is stuck open. I will see if the dealer will give this under warranty but I'm curious, anyone do thermostat deletes and regret it? From what I read, the TCM wants 200F or close to it for better shifts and this is why the thermostat is there in the first place. On the other hand, living in a warmer climate where it doesn't usually get below 40-50F, could leaving this thermostat open extend the transmission life?

I got the dreaded P0700 & P0711 on Monday on a 2015 GMC Yukon Denali. Cleared the code and it came back. MIL hasn't iluminated yet so I'm waiting on another drive cycle before I schedule an appointment with the dealer. In the meantime I wanted to understand the conditions of P0711. GM has a great PDF but I can't quite understand it. https://gsi.ext.gm.com/gmspo/mode6/pdf/2015/15OBDG08A Transmission Diagnostics.pdf I don't quite understand how to apply the table to the conditions. Further to add confusion, my scan tool is reading -40F for TFT although in tow mode my transmission temp reading hovers between 125 and 150. I did watch it once and see it dip to 100 flat from 125-150 for a brief moment so I imagine its just a flaky sensor but I'm more curious about what triggers this based on those conditions.

First thread on here, hope it helps people. **!!** DISCLAIMER **!!** Yes i know this is an 8 spd and its supposed to feel different than other automatic transmissions. AND Yes, I know these transmissions had a lot of issues out of the factory. **!!** DISCLAIMER **!!** Looking to find out information/recommendations for full fluid flush (cooler and all) and filter change for 2016 silverado 1500 with 6.2L and 8spd with max trailering pkg (which i think makes it an 8L90, havent confirmed yet) with almost 90000 miles (maint schedule from chevy for 2016 says trans/tfr case/diffs fluids due at 90k). I have a hard shift from 1 to 2 at very low speeds sometimes (especially when cold, but that makes sense because fluid dynamics), basically parking lot driving. I also have a weird deceleration when up to temp when taking off from a light less than 1/4 throttle, going from 1 to 2. Its almost like its slipping too long between 1st and 2nd. My body physically moves forward due to what feels like pushing the clutch in during acceleration. No banging or loud noises, just noticeable loss in acceleration. Just bought the truck at 88750 miles. If it matters, it has had PCM warranty reflash in the past, not sure based on garbage maintenance records if a flush had ever been performed. What I know: Dealership quote (Milwaukee, WI area) before 10% discount: - Gasket $36.21 - Filter $30.17 - Fluid $170.20 (represents 20 qts., *not sure if capacity or thats just how much they use when flushing*) - Labor and shop supplies $546.29 (this price makes me think that it is more than just a flush, like they are opening the system and forcing fluid and or cleansers through all components that touch trans fluid to make sure its fully flushed/cleaned. if just flush where they hook up to machine, this is such a damn rip off) Transmission fluid I am supposed to use to avoid shuttering or issues due to moisture absorption that was initially experienced according to GM TSB# 18-NA-355 (*PLEASE LET ME KNOW IF THIS IS OLD TSB#*): - (*HAS TO BE WITH BLUE DOT, NOT BLACK DOT) Mobil 1 Synthetic LV ATF HP It has never had the fluid changed before to my knowledge I'm trying to figure out what the latest GM factory procedure (either with a TSB# or whatever work order code is used) is so that I can communicate to multiple dealerships nearby so I can get pricing on actual same services. Here is the link that describes it a lil more and shows the fittings that they put on transmission for flush: https://gm-techlink.com/?p=11127 And here is another about the TSB for fluid (this one is more recent than the one above): http://gmauthority.com/blog/2019/08/tsb-seems-to-fix-8-speed-automatic-gm-transmission-problems/ I plan on getting a fluid sample of the transmissions fluid from dealer prior to changing so that I can send it out and get it tested so I have a record. (I will post the results of tests here when I get them). I got my free test sample bottles from Blackstone Laboratories (If you or your friend has an in with GM engineering and/or happens to know the pass/fail criteria that they use to decide whether or not to cover transmission or torque converter replacement, please let me know. I'd like to know what to look out for when I get my results from fluid testing) This is the most expensive thing I have ever purchased, i have extended warranty on it just because I'm worried about the transmission and obviously all the electrical doodads that new vehicles have nowadays, I just want to make sure I am taking care of it correctly. Would love to hear from seasoned GM certified techs and/or ASE master mechanics/techs and/or GM Engineers. Also please chime in with prices you've experienced including general location you're from so I can get an idea if this dealer is trying to rip me off. (so far the only thing I dont trust is the labor/shop supplies in the quote above, depending on what the procedure is)