2018GMC

23K miles on my 2018 sierra crew cab 6.6’ bed 4x4 6.2L 8L90. no, I haven’t been in prison for the last couple years or ever. I have multiple vehicles and might have a problem lol. Dealer replaced negative battery cable right before the bumper-to-bumper warranty was up due to occasional odd messages immediately after starting like service stabilitrack, Airbag, etc. Even after the negative battery cable was replaced due to it testing high on resistance. I still would see these messages messages occasionally right after start up. Replaced the battery. messages almost never show up although just when I think it’s really fixed I’ll get a message after a few months. Seems the only happen if I restart truck after a brief amount of time like after refueling. Engine and Transmission have been fine. I at home flushed the 8 speed with the new fluid at 18k miles. Drivers window rattles when closing the door. Only if it’s rolled up all the way. If I tap the down button just a touch then no rattle.

Videos of the suburban on my channel along with some other vehicles in the family fleet. DocTube - YouTube

Since you don't have the max tow package, your truck is probably 9200lbs since you have the 6 speed and 3:42 gears. My 2018 CC 6.5' bed 6.2 4x4 has the 8 speed and the max tow package with 3:42 gears. Normal gearing with 8L90 is 3:23. Max tow package and 6 speed you get 3:73 gears. My tow rating is 11,800. I wound never want to tow that much with a half ton. Like others have said, tow 75% or less of what it is rated for. If your truck is rated at 9200lbs it should tow 7000lbs ok, especially with a weight distribution hitch.

FYI - Best price for Mobil 1 Blue label Synthetic LV HP ATP 124715 $46.49 https://www.amazon.com/gp/product/B086R9GDV1 Make sure it is sold & shipped by amazon. I have ordered twice an both times received the blue label even though the product page pictures the old black label.

I hear ya. I changed the fluid myself, did the driveway flush and exchanged 12qts with the new blue label fluid. My 2018 only has 23K on it but I wanted to change out the factory fluid that can absorb moisture. I still get the odd clunky mixup shift every once in awhile in stop and go traffic but I’ve never had the shudder issue and don’t want to experience it.

@Grumpy Bear Thanks for the detailed explanation.

Anyone install the STL010 or updated GM transmission thermostat? I don’t want to do the pill flip because I live in an area where we get below freezing temps and 4 full seasons. Not sure if my 2018 8L90 has the updated part. It’s hard to read what number is stamped in the trans thermostat. my trans temps are always 180 - 200 during the summer and maybe got to 205 when crossing the desert with outside temps 115 - 118 https://static.nhtsa.gov/odi/tsbs/2021/MC-10207911-9999.pdf

I have a 2003 suburban z71 with factory 6 disc in dash cd receiver. When it’s colder than 50 degrees the radio powers on but now sound or door chime until the cabin warms up. Summer months it works fine. Cold months nothing the you hear a pop and you get sound. I’ve tried replacing the Bose amp (under the center console) pulled from a junkyard Tahoe of same vintage. Still same issue. Also tried reflowing solider in the main circuit board on the radio receiver and my original amp. Still no change has the no sound when cold. The random theftlock seems new but it self heals and goes away within a few seconds. Only happens very rarely. The random radio powering off then on is new. Anyone else experience this? Is there a known wiring harness issue under dash or center console? My burb has the sunroof, maybe in the past 20 years someone left it open and it rained? Although switching out the Bose amp didn’t seem to fix anything. Also get codes Radio DTCs U1000 Class 2 Data Link Malfunction U1016 Lost Communication with Powertrain Control Module U1151 Loss of VIU Communications U1167 Lost Communications with Rear Seat Audio/Rear HVAC BCM DTCs U1000 Class 2 Data Link Malfunction

I usually run bilstein 4600 for stock height trucks. Recently put KYB monomax on 03 suburban they are 1” shorter than stock which may be ideal for you. I had to add a 1” spacer to the fronts to get full suspension travel. Monomax ride is noticeably firmer than bilstein 4600 but not harsh. Helps firm the old burb up.

I sent the engine computer to Blackbear performance and they put their 87/89 tune on. I left the tow haul button alone since I occasionally tow 3500lb enclosed trailer. After the tune there is more getup and go, trans shifts are firmer and it revs out a bit more over stock, like 5600 / 5700 rpm. Apparently they have a high octane tune for max performance but I didnt opt for that since I don't want to put premium in all the time and its a big heavy suburban after all lol. After the tune, maybe I gained the 10 hp the later engines were advertised with. I live at 7k foot elevation so there aren't any dyno places by me but with the tune, afe intake, and magnaflow muffler, i've done the "easy" performance upgrades.

Took all day to cool down to 110 but on a level surface, idileing in park, i drained half a quart out of the 10mm check plug. I put the plug back in when the stream slowed to a thin stream / spotty trickle. Should I leave battery disconnected overnight or a few hours since I put the new fluid in? Does this reset the transmission shift learning? I don't have shudder issues but I do have the occasional lurch in park when cold and sometimes harsh engagement when shifting into drive or reverse. Very cold winter temps there is the rubber band feeling when accelerating from a stop but once engine and trans warm up no issue. Summer driving and towing no issues.

Propane torch on the surrounding area and hammer the side. Not sure if you are in the rust belt but heat and hammering the side not directly on the ball joint is what helped me. Sounds like yours may be heavily rusted and now one part. Try a different penetrating oil like Deep Creep. Deep Creep | Premium Penetrating Oil & Lubricant for Shop & Household (seafoamworks.com)

I posted this question on TahoeYukonForum, no one had a definate answer but the two theroies were. 1.The switch to electric fans from mechanical. along with more powerful P59 Engine Computer. 2.The LM7 did not have a separate high and low octane table in the tuning. The L59's high octane table had more aggressive timing......and that is where the power increase is from. But only if it determined you put premium in it (it determines this by not hearing any knock while trying to run the most timing it can get away with)

My internet research points out: LM7 isn’t flex fuel compatible and that’s the main difference between LM7 and L59 according to multiple posts. They are 99% the same. I realized this past weekend that I've had an L59 the whole time I thought it was an LM7. Only differences are more injector flow (33 lb/hr vs 22.5-28, depending on the year iirc), different fuel injector connectors (EV6, I believe, vs minitimer), and a few differences in the ECU. Depending on the year, it got a sensor to detect the ethanol content of the fuel, and also depending on the year, it kept return rails longer than the non-flex fuel motors did. Besides that, it is literally the exact same motor. https://rxmechanic.com/l59-vs-lm7/ L59 Vs. LM7 Engine : What’re the Differences? | Rx Mechanic The factory L59 injectors were rated at 33-36 lbs. and support about 435 hp at the wheels. Note the 2001-04 return style fuel system cam with 33lb injectors running at 50 psi, while the 2005-07 engines were returnless and had 36.6lb @ 58psi injectors. The easy way to know which you have is the 2002-04 rails were plastic and the 2005-07 rails were stainless. https://www.onallcylinders.com/2018/10/12/l59-5-3l-engine-upgrade-guide-expert-advice-l59-mods-maximize-performance/