Transmission shifts awful

[Kspinazzola]

6 speed trans (5.3L) on my 14 Silverado shifts like crap. Hard downshifts constantly random thumps even when driving and not shifting, just overall bad performance. Weird thing is I had a remanufactured trans put in the truck a couple months back. It shifted like crap before the swap but worse. New trans is an improvement but still sucks. Engine runs fine except code for bank 2 cat below efficiency. But if I clear that it takes a few days to come back so I doubt the cats clogged that bad. I doubt that’s causing my trans issues. 
Other Chevy owners I talk to say “that’s just how the 6 speed is” but I’d say mine is definitely worse than average. 
when I’m driving and engine is at lower rpms it almost feels like it’s stumbling a bit. Kind of like if you were in a manual car and shifted up too soon and started bogging down the engine. Rpms look normal tho.

anyone have any advice on what to check out? I love everything about this truck except the awful shifting if I can’t figure it out soon I’m honestly just gonna sell it which sucks. 

[JacobC1983]

I felt the same thing in my 2015 and 2016 6 speeds with the 5.3.  I was happy to get rid of them.  

[silveradosid]

the clogged cat is your problem, clearing the code does not help because the code will still stay in the computer as a pending code until there has been a certain number of ignition cycles without the problem. you have half of the engine that is running under spec

[BO TIE 1]

6 speed trans (5.3L) on my 14 Silverado shifts like crap. Hard downshifts constantly random thumps even when driving and not shifting, just overall bad performance. Weird thing is I had a remanufactured trans put in the truck a couple months back. It shifted like crap before the swap but worse. New trans is an improvement but still sucks. Engine runs fine except code for bank 2 cat below efficiency. But if I clear that it takes a few days to come back so I doubt the cats clogged that bad. I doubt that’s causing my trans issues. 
Other Chevy owners I talk to say “that’s just how the 6 speed is” but I’d say mine is definitely worse than average. 
when I’m driving and engine is at lower rpms it almost feels like it’s stumbling a bit. Kind of like if you were in a manual car and shifted up too soon and started bogging down the engine. Rpms look normal tho.
anyone have any advice on what to check out? I love everything about this truck except the awful shifting if I can’t figure it out soon I’m honestly just gonna sell it which sucks. 

Get a handheld tuner. I know Diablo has tunes for the six speed. I have one on mine and it shifts great. If your not comfortable doing it yourself take it to someone that can tune it for you.

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[newdude]

Fix the cats and re-test.  

[It's Tim]

Is this a salvage vehicle?

[dgstarr63]

I had a 2015, 1500, 5,3, 6 speed. 3.42 axle, 4x4 until it was totaled in an accident last fall with 54,000 miles.  This transmission was the best transmission that I have ever had in any vehicle. Now I have a 2021 with the  8 speed and wish it had the 6 speed.

[CamGTP]

A P0420 or P0430 doesn't mean the cat is plugged, why do people always jump to that conclusion. Many vehicles could drive for 100k miles with that code and not have a single problem.

 

Get a tune for the truck and it'll completely change how it drives.

[newdude]

On 4/12/2021 at 8:18 PM, CamGTP said:

A P0420 or P0430 doesn't mean the cat is plugged, why do people always jump to that conclusion. Many vehicles could drive for 100k miles with that code and not have a single problem.

 

Get a tune for the truck and it'll completely change how it drives.

 

A tune completely ignores the bank 2 efficiency issue he has and would be a band aid on the real issue going on.  He can clear it and it comes back in a couple days. 

 

Why does everyone jump to conclusion and say get a tune?  

[CamGTP]

12 hours ago, newdude said:

 

A tune completely ignores the bank 2 efficiency issue he has and would be a band aid on the real issue going on.  He can clear it and it comes back in a couple days. 

 

Why does everyone jump to conclusion and say get a tune?  

The tune was is regards to the transmission and not the cat code. That was the main complaint he had and title of the thread.

[swathdiver]

On 4/12/2021 at 4:43 AM, Kspinazzola said:

6 speed trans (5.3L) on my 14 Silverado shifts like crap. Hard downshifts constantly random thumps even when driving and not shifting, just overall bad performance. Weird thing is I had a remanufactured trans put in the truck a couple months back. It shifted like crap before the swap but worse. New trans is an improvement but still sucks. Engine runs fine except code for bank 2 cat below efficiency. But if I clear that it takes a few days to come back so I doubt the cats clogged that bad. I doubt that’s causing my trans issues. 
Other Chevy owners I talk to say “that’s just how the 6 speed is” but I’d say mine is definitely worse than average. 
when I’m driving and engine is at lower rpms it almost feels like it’s stumbling a bit. Kind of like if you were in a manual car and shifted up too soon and started bogging down the engine. Rpms look normal tho.

anyone have any advice on what to check out? I love everything about this truck except the awful shifting if I can’t figure it out soon I’m honestly just gonna sell it which sucks. 

Fix the cats and whatever killed them and then give the transmission a chance to run right.

 

The 6L80 is an awesome transmission.

[pokismoki]

i would start with getting the tcm reflashed with the stock file first, then take the next step.  you might have some crappy trans tune, or a poor rebuild. find a local tuner.

Edited April 17, 2021 by pokismoki

[Kspinazzola]

On 4/12/2021 at 7:45 AM, silveradosid said:

the clogged cat is your problem, clearing the code does not help because the code will still stay in the computer as a pending code until there has been a certain number of ignition cycles without the problem. you have half of the engine that is running under spec

I thought the same man but I did my research and that code can be tripped by as little as a 5% change in the O2 sensor reading. Not sure why but over the winter the code went away on its own multiple times. And if cleared would take days or weeks to come back. Leading me to believe it’s not clogged very bad so I didn’t think that was my issue. If you think it is my issue is there a way to check? Or a way to replace cat without spending crazy money on a truck with 160K, lol

when I get under it and hit the cat it’s normal, no rattle or indication the insides have come apart. 

[Kspinazzola]

On 4/12/2021 at 7:48 AM, BO TIE 1 said:

Get a handheld tuner. I know Diablo has tunes for the six speed. I have one on mine and it shifts great. If your not comfortable doing it yourself take it to someone that can tune it for you.

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I had a tune for a bit and it didn’t help and honestly I didn’t like it. Ended up going back to stock after about 2K miles

[Kspinazzola]

On 4/17/2021 at 10:41 AM, pokismoki said:

i would start with getting the tcm reflashed with the stock file first, then take the next step.  you might have some crappy trans tune, or a poor rebuild. find a local tuner.

The shop that installed the reman unit told me they would flash it stock. The reman company seemed pretty reputable but the shop that installed turned out not to be lol