swathdiver

AC Delco OE or Professional. Preferably the former 748GG with Delphi Coils, 748HH with Melco Coils.

Most manuals say to change it every year if you don't hit the mileage. Mine is lubed by plain old Mobil One synthetic and you can feel the difference between fresh clean oil and 5,000 mile oil. I used to run a Jiffy Lube and conventional oil back then was dead by 5000 miles. To each his own.

Do you see the numbers 799 or 243 on the cylinder heads, facing the sides but at the front of the engine? If you see 862 or 706, those are for the LM7 and L59.

I wouldn't suggest any Seafoam. Look in your glovebox door for the RPO sheet and look at the "L" codes. You might have an LM7, L59 or L33. Yellow gas cap (if original) also indicator of FlexFuel engine. Here's the little bottles I've used from Wally World: https://www.walmart.com/ip/Super-Tech-Concentrated-Fuel-Injector-and-Carburetor-Cleaner-6-oz/16821284 Is your gas mileage suffering? If not, this may be much ado about nothing.

If you have an L59 FlexFuel motor, run E85 for a couple of tankfuls. Alternatively you can run Chevron's 93 with Techron for a couple of tanks. Those little $2 bottles of Super-Tech Fuel Injection Cleaner at Walmart have helped mine some too. Before that we used to use GMs cans of Echlin and attach them to the fuel rail and run the motor off the can until empty.

I thought GM stopped using whale oil sometime in the 1950s or early 1960s; whenever the Hydramatics were introduced. Dexron VI came out around 2005 or so, I had an '06 Montana that was spec'd for it but not the '04. But you're right, there were other synthetic transmission fluids before then. I am not familiar with these terms, group level fluids, will have to look that up and check out Redline again. No thermostat on the GMT900 transmission. My particular truck has the K5L, Enhanced Cooling Package with the KNP, external transmission cooler. The thermostat is called a 187 degree. Begins to open at 188 and is fully open by 206. Most of the time the temperature is rock solid at 192 but have seen it at 196 a couple of times. I considered putting in a lower temperature but wanted to learn more about these modern systems. In the old days that was the first thing we did, cut off the hot water to the intakes and throttle bodies, vented the valve covers and put in 160 thermostats. My 425 RWHP Buick GN drove around at 154 with a 160 thermostat unless we were racing, and that was during summer.

So is the oil pump running while the motor is off? These new trucks have start stop and AFM/DFM. The Hybrid was made for the task with a larger starter motor while other vehicles use the original type starter motor. A better way of saying is that one was built for the task and the other was adapted to handle it. The former is more durable than the latter. The GMT900 hybrids had start/stop tech and their 2ML70 transmission had two 60 KW electric motors one of which was used to start the engine. We rented a Chrysler Pacifica with start/stop and I did not like it either. Took too long to get moving, felt like a golfcart. The dial shifter was an even dumber idea. Not being used to it, I left the car in gear twice when I thought it had been placed in park.

2009 GMC Yukon XL. Z82 does not determine whether or not it has the transmission cooler. I think for yours it would be part of NHT package but it could also have it separate, not sure. Anyways, the RPO code for the external trans cooler is KNP.

Read the shop manual for the latest numbers on your K2. For the GMT900 with same transmission, the normal operating range is between 160 and 200 degrees. The high temperature alerts and codes don't happen until the fluid gets to 266 and 270. Mine, with 3.42 gears and the factory external cooler runs 156 @ 92 outside while running 75 mph and will climb to 176 once off the highway. The only time it's been higher was the day the fluid exchange was done and it was 100 degrees out and while drag racing.

Does that chart pre-date synthetic fluids? I posted this on another forum with regards to the 6L80E used in the GMT900s: 2007-2014 GMT900 SUV The 6L80s normal operating temperature is between 160 and 200 degrees. This corresponds with the HOT check on the dipstick when checking the fluid level. Cold check temperatures are between 80 and 90 degrees and also have a corresponding mark on the dipstick; mine anyway. The temperature range for the Service Fast Learn Adapts procedure is 158-212 degrees. If the transmission's temperature reaches 266 degrees for 5 seconds the "Transmission Hot Idle Engine" warning will display on the DIC. Code P0218 (Transmission Fluid Overtemperature) will set if the fluid is greater than 270 degrees for one minute. On a side note, the shop manual says trailer towing should occur in D4 to ensure the cooling system functions normally. The Flash Point for AC Delco's Dexron VI fluid is 401 degrees. There is a transmission oil life monitor within the Transmission Control Module and is visible and able to be reset with the Tech2. I reckon that it is also based on engine revolutions and transmission temperature, similar to the Engine Oil Life System. As for operations, while driving on the highway at 75 mph on a 92 degree day, the transmission temperature will be 156 degrees. Same speed at 82 degrees it will be 151 degrees. Coming off the highway and into stop and go traffic it will climb into the 170s (176 usually). The day the fluid was changed, and driving home from the dealer, it was over 100 degrees outside and driving in stop and go rush-hour type traffic, the temperature crept up to 196 but never got close to that again. The internal fluid life monitor still said 27% if memory serves when the fluid was changed at 117K. I have pretty good records from the previous owner but none showing transmission service. Approaching 130K now, the transmission oil life monitor still has it in the 90s last time I checked. I am thinking of sending a sample off to Blackstone-Labs.

No, it's our rainy season. They now make them where you don't have to use JB Weld and wait 24 hours anymore. I'll probably do it in October or November.

Well, it was a 2019 LD, same truck as 2018! Not the new one. Don't see anything about the new one. Wait and see until the correct specs come out. All kinds of mis-information was flying around before each new style has been released. GM has always sized their larger cars and trucks for the most part to get 300 miles in city driving.

That was fine for Jimmy Carter's 55MPH speed limit. Now everyone wants to pull a travel trailer as fast as Sammy Hagar.

Gotta be a problem with his programming! What is happening to that poor guy is nonsensical, especially since you have direct comparisons. They gotta comply with those stupid CAFE regulations. The President stopped them from getting crazier but they need to roll them back and really, get rid of them altogether and let the public decide. Barring that, at least leave the trucks or trucks equipped with 4WD/AWD alone. 4LO for most folks is nice to have, like having 4WD is nice to have but not absolutely necessary for most folks in the south. I use mine to exercise it lest it jam up from lack of use.

Chevrolet's website says 26 gallons for Crew Cab Short Bed 1500. That's a highway range of about 500 miles before the light comes on.