6l90 - overheats in every gear but 6th

[wanarace]

2008 Sierra 2500Hd 6.0l 4x4

 

Overall shifts and works fine. A little slow to shift and sometimes flares for 30s if you drive away after initial start up. But that's it.

 

Highway driving provides the best example. If I am driving on flat ground at 100km/hr (60mph) tranny temp will be around 65C (150f) in 6th gear. If I manually put it in 5th or 4th the temp starts climbing at a rate of 1 degree C every 10s. In a mile (1.6k) the temp will be up over 10 degrees C and keep climbing rapidly until I drop it back in 6th and the temp will slowly start dropping again.

 

In the city, it will run around 210f in traffic on a 75f day. It not an airflow issue, I am running a new extreme duty fan clutch (mechanical fan on this truck) and it sounds like it is always locked up.

 

Anyone run in to something like this before? Any chance a sonnax zip kit will fix the issue?

 

Thanks

Steve

 

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