GM 6L80 Transmission Shifting Issues...

[Arctic Slalom]

I've got a 2012 Suburban 1500 4wd with 6L80 Transmission. The truck has 208K miles and is in great shape (I've very particular with service). I NEVER abuse the truck, and it pulls very, very little (only the Malibu down to public access and to town (winterize) a couple times a year. I live in the mountains of WNC (Asheville).   

I changed out transmission fluid at 70K, 135K, 190K and now the truck has developed a bit of a "shudder." When it's cruising at 70 mph (or so) it will drop/climb 200 RPM to maintain speed. It seems like it's most evident at lower RPM's (1200-1600). It almost never shudders above 2000. I noticed this for the first time last week.  

I'm guessing it's my torque converter or perhaps the torque converter clutch which is on the brink of failure... 

My local mechanic (who I trust) says ~$1200 for a new torque converter or about ~$3200 for a new reman transmission. The truck is NOT throwing any codes which he can find. 

My questions:

-If I install a new torque converter, should I just "bite the bullet" and rebuild transmission? 

-Will it be a waste of money to only do the Torque Converter? 

-Is there a "better" reman transmission out on the market? 

-If I rebuild the transmission what it realistic expectation for my 5.3 engine mileage? Truck has 5400 hours on it now. I'd like to keep this truck as long as possible because: it runs great, it's comfortable, it's paid for and a new burb is like $80K.   

As always, this forum seems to have well thought out responses, which I appreciate. Thanks in advance!  

[EchelonMike]

Are you sure it's the transmission and not cylinder deactivation kicking on and off?  If you switch the display on the dash to show when it switches from V8 to V4 mode, is that when the shudder happens?  I always felt like my 2007 and 2016 Suburbans "rumbled" at lower RPM when flipping between V8 and V4 modes in the 5.3L.  Wondering if it's something other than the transmission if it's only happening at lower revs?  

Assume you checked fluid levels in the transmission.  

[MLA]

36 minutes ago, Arctic Slalom said:

I'm guessing it's my torque converter or perhaps the torque converter clutch which is on the brink of failure...

I had long since left the wrench turning profession by time the 6L80 came out, so I know little about it from a technical point. However, your description smells like an engine miss. Low RPM dues to being in high gear with enough throttle input, and you get a tremendous load on the secondary ignition. I would love to watch the scan data live while this is taking place. 

My 03 Tahoe with a 5.3 FLEX has 310K on it and is my daily work driver. However, I did replace the 4L60 at 295K after a catastrophic failure. For what its worth, someone had replaced the converter and some other internal repairs, likely attempting to resolve what ultimately lead to the failure.     

[Arctic Slalom]

58 minutes ago, EchelonMike said:

Are you sure it's the transmission and not cylinder deactivation kicking on and off?  If you switch the display on the dash to show when it switches from V8 to V4 mode, is that when the shudder happens? 

I don't think it's the AFM switching; I'm familiar with the AFM going from V4 to V8. My AFM transition is still buttery smooth between these two (very hard to tell). I actually watched this the other day. (2) weekends ago went from Asheville to Charlotte and this past weekend went from Asheville to Nashville with family. Yes, the transmission oil level it right where it should be (checking it warm, idling with level vehicle). I've used the GM Dexron Fluid @ 70K and 190K. The 135K swap was BG fluid exchange.  

The motor runs and idles smooth. It still pulls plenty strong. Religiously use Mobil1 synthetic and change at 15% oil life indicator. Changed plugs at 100K and 200K. 

 

[Arctic Slalom]

1 hour ago, MLA said:

My 03 Tahoe with a 5.3 FLEX has 310K on it and is my daily work driver. However, I did replace the 4L60 at 295K after a catastrophic failure. For what its worth, someone had replaced the converter and some other internal repairs, likely attempting to resolve what ultimately lead to the failure.     

How many miles where on it when you bought it? Just curious about how long your original converter lasted? I'd love to get my suburban over 300K; which I think is def possible. 

[MLA]

12 hours ago, Arctic Slalom said:

How many miles where on it when you bought it? Just curious about how long your original converter lasted? I'd love to get my suburban over 300K; which I think is def possible. 

Just looked at my maintenance log. I got it with 294K and replaced the trans at 298K to be exact. The converter in the old trans was very clean so I speculate it was not in there long. 

[Arctic Slalom]

I had my existing transmission in 2012, 1500 suburban rebuilt. New TC and rebuilt all the worn parts. That was at 208K and now it's close to 240K. 

truck still runs great.