Super hard shifts-08 Denali

[optimusprime]

2008 Yukon Xl Denali with 206k on the clock.

For as long as I can remember, I have had a super hard ”slamming” type shift from 2-3 and going around 20-25 mph. It happens around 85% of the time leaving the house when the truck isn’t very warm and randomly thereafter.

Along with that, I also get the same type of super slam shift when I floor it at higher speeds (merging traffic or trying to pass). Happens around 70% of the time in this situation.

Any thoughts as to what could be causing this?

 

[Marky Dissod]

When was the last time you changed your ATF & filter?
Hang on, let me try the batsignal ... @NickTransmissions ...
If it's been a while, when you go to change the ATF & filter, you'll likely be changing other things too.
With luck, Nick will tell you what needs changing.

 

[NickTransmissions]

2008 Yukon Xl Denali with 206k on the clock.

For as long as I can remember, I have had a super hard ”slamming” type shift from 2-3 and going around 20-25 mph. It happens around 85% of the time leaving the house when the truck isn’t very warm and randomly thereafter.

Along with that, I also get the same type of super slam shift when I floor it at higher speeds (merging traffic or trying to pass). Happens around 70% of the time in this situation.

Any thoughts as to what could be causing this?

Scan codes, check fluid levels to cover those bases but, assuming you have the correct amount of fluid in the system and no transmission-related codes or throttle position sensor, MAF or other engine management codes have been set/stored, I'm thinking your 3-5-R clutch drum is leaking real bad and that clutch pack is in the process of burning up. The hard shift is due to TEHCM seeing the slip and maxing the line pressure when shifting into 3rd to compensate.

Torque converter is also high on the list of suspects though usually failing TC symptoms present across multiple gear transitions, not just 2nd to 3rd.

Smell the fluid on the dipstick - if it smells burnt, drop the pan and see if lots of burnt clutch material is present...If so, put the pan back on with a few bolts and yank it for overhaul....Visit my 6L80 Information thread for rebuild resources, tech manuals, videos, etc - link is in my signature line.