Rusty Shackleford

244k on my '18 1500 2wd 5.3. On it's third 6l80e, first one gave up at 97k, second one at 187k. Have replaced other things like water pump, t-stat, coolant surge tank, and normal wear items like brake pads, plugs, etc.. I threw a P0420 code last weekend, will mess with it this weekend and see if it the cat or O2 sensor. Have a front strut making a little noise on bumps and turns with the suspension loaded, so fronts will get replaced pretty quickly. The biggest concern, however, at this time is that my oil pressure has dropped a little bit from normal and I'm getting a slight lifter tick from the odd bank. Might be doing a rebuild pretty soon, we'll see. If I do, the junk JMBX torque converter will get replaced with something that won't eat itself and destroy the transmission. Overall, transmission issues aside it's been a pretty dang good truck. I would have traded it in by now except for outrageous new truck prices and reliability issues. At this point I think I'd rather work with what I have instead of taking on something unknown for so much more money.

Switch the Bank 1 O2 sensor with the Bank 2 sensor, see if the problem moves to Bank 1. If it doesn't, your problem is not the sensor itself. Then your looking at harness or cats again.

Yep, just went thru this too. Coolant temp sensor and t-stat replaced. Cleared the code, and problem solved.

How are they checking it? If flexing the wheel/tire while in the air, and finding movement, it could be the wheel bearing assembly. If so, it's not long for this world anyway.

I agree with Karnut. Pull your 5.3, freshen it up, add a mild cam while doing so, then optimize that setup with some bolt-ons and tuning. Focus on torque numbers in a usable rpm range, forget HP numbers unless you want to race it.

Well, I'm on my third transmission due to GM's junk torque converter. Both replaced in warranty, 1st one made it 97k miles, second one gave up at 187k miles. When they installed the current one they did the tsb and it dropped my operating temp to the prescribed 145ish range, but in Tx summer traffic or heavy towing the temp would still creep up into the 180's and take forever to cool off once I got moving again. Often taking an hour or more to drop back into the 160's. I average about 50k miles a year, my truck is my 2nd home. Back in June I installed this kit ( https://www.amazon.com/WHATEVER-TAKES-TRANSMISSION-PARTS-STL010/dp/B0BCL9M23T/ref=sr_1_2?crid=FSXXUFT1XO12&keywords=superior+products+transmission+bypass&qid=1701636535&s=automotive&sprefix=superior+products+transmission+bypas%2Cautomotive%2C159&sr=1-2 It retains a bypass function and eliminates temp regulation. Took about 30-45min's. I also installed a Hayden cooler under the cab (w/fan) that runs constantly. My trans temp in the summer now still operates in the 140's (seems like that's just where it wants to be), and creeps up into the 160's under loads and in traffic, but cools back down quickly when I traffic breaks loose and I get some air moving. I haven't seen it get over 190 since, not even towing the trailer and tractor 100 miles in August. I went from burnt fluid every 25-30k miles to fluid that still looks and smells new at 50k. It baffles me that anyone at gm would think running an auto transmission at 180+ degrees constantly (and regularly well over 200) was a good idea. On top of that, let's merge the trans cooler with the ac condenser coil so it conducts heat into the transmission when the ac is running, then hide all of that behind a stupid set of louvers/shutters that can, and do, close and restrict airflow. Add in the previously mentioned junk converter and it's way beyond "if it fails". All to gain a few tenths of a mpg. There ought to be a class action suit on these things. I'm going to pull the trans and replace the JMBX converter with something that doesn't eat itself over the Xmas holiday, might have the trans gone thru but will at least have a tuner change some things up on it afterward to help it. I'm currently at 244k miles so will be doing everything I can to make this one live longer. I'm in the infancy stages of planning a 6.2 swap around 300k, if it lives that long. I have no complaints about the L83, it has been dependable so far in original form, but I sooo love the LS3 in my 5th gen Camaro.

I guess I'll jump in on this one if y'all don't mind. A little background, '18 Silverad 5.3/6L80E 2wd. Bone stock. Bought the truck new with the express plan of leasing it to my company on a mileage basis. I drive a lot for work, average 50k miles a year. The truck drives at about 40-50% payload all the time (tools and what-not). Some personal use towing the boat and stuff, never even approaching what it should be capable of. Mostly highway miles though, commuting daily 50miles one way to and from the office, or on road trips. To date the truck has seen about 32 states, and lives in Texas (for weather reference). 1st converter failed at 97k, took the trans with it (as it will do), while under a crappy 100k extended warranty. EW company wanted to put an LKQ (used) transmission in it, I ended up paying $1k out of pocket to get a crate trans installed because it came w/100k warranty. No TSB at this time, dealer put the 190f stat back in it and I didn't know any better at the time. Factory service at 48k on the 2nd trans showed almost clear fluid, but definitely smelled toasty. TSB might or might not have been out around this time, I will give them the benefit of the doubt by saying it wasn't. 187k, 2nd converter goes and takes the trans with it (as it will do), and dealer replaces it, charging me like $125 for incidentals, and installs the 145f stat. So far I'm making out like a bandit, 3rd crate unit in for less than $1,200. But in 13k miles she's all mine, no warranty on the latest transmission. Now, I never paid much attention to trans temps until the latest one got installed. But my dash now lives on this screen. Last summer I saw road temps over 100f more days than I can remember, often exceeding 115f. Open road driving with the 145f stat I could hold in the 170's if I kept it under 70mph, 75-80mph pushed trans temps into the 180's, and 85mph made it run high 180's to mid 190's. In town, stop and go summer traffic, 180's were the norm. Yes, we have roads in Tx up to 85mph speed limits. I decided to leave everything alone thru winter, but recently did the Superior kit STL010, about 2weeks ago. While we have yet to see summer conditions, I am seeing that the stat delete will not make a bit of difference once the oven is on. But it does take significantly longer to get up to temp from a cold start. I've seen temps down to the low 40's since the delete, while it takes a bit to warm up I don't have any shifting issues, and once up into the 130's it tends to remain there or higher. My next move, possibly this weekend, is to put and derale fan/cooler under the bed tapped in the return line from the front cooler, and switch it at 160 on/145 off. In a few weeks it is getting a billet converter, new pan w/drain plug, and amsoil fluid, etc. I'm researching what's involved with the r&r now, will do it all myself. Will also get some programming done at that point, talked to tuner that says he can also make some improvements that should help, as well as change a few other little things I want done while in there. I'm at 230k miles on the truck now with no other major issues. I've deleted the unnecessary blades from the grill shutters to eliminate a spiking engine temp issue on the freeway, done plugs/wires, replaced the water pump/eng stat, uca's & lbj's, been thru a couple of batteries, several sets of AT tires, nothing that shouldn't be expected for the mileage. The oil drain plug starts quivering if I just bend down next to the truck. Valvoline high mileage 0-w20 comes out only slightly darker after 6k miles, and it drinks about a half quart between changes as it always has. I do love my truck, and take good care of it. I just wish Chevy hadn't used us owners as the R&D dept for their transmissions. Anyway, sorry for the novel, will chime back in when I get the cooler installed. My goal is to keep the trans as cool as I possibly can (within reason) and if I start having shifting problems then I'll take a step back.

Had this issue when I got my 2018 w/6spd. Talked to the trans guy at my dealer and he told me to run it in tow/haul every time I drove it for about two weeks, then revert back to normal. It largely solved the problem. I get a hard downshift about once a week now, much better than it being a daily occurrence.