Frequent harsh downshift 2-1 HD 3500

Cavepeople

Newbie
Joined
Jul 12, 2021
Messages
2
Points
1
Make
Chevrolet
Model
3500HD
Year
2008
Miles
129000
Engine
6.6 Diesel
Good day..Vehicle info: 2008 Silverado 3500HD Dually 6.6L w Allison 1000 trans. 129,000 miles. Vehicle has a lift with the 22.5" semi wheel kit; only mentioning this in case the large tires and wheels have something to do with it. Issue: at times it has a harsh downshift from 2nd to 1st. It clunks hard when downshifting. At times it's smooth without issue. All gears up shift great 1-6. New fluid and filters. Has PPE deep trans pan. No codes being thrown. Any ideas?
 

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bp042665

hunting nut
Joined
Nov 26, 2012
Messages
721
Points
18
Location
Iva South Carolina
could have a valve issue when its hot try lube guard platinum additive and drive about 300 plus miles also if able to watch live data pay close attention to input and out put speed sensor's for a glitch
tps can also have a glitch that can cause this have seen all 3 of this in the allision transmission
 
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