Seems like transmission is slipping when cold

[LMTV89]

Im not sure if this is a temp issue but recently since it's gotten into the 40's here when I first start the truck after a 5 min warmup the transmission is slipping and barely moves the truck, going from N to 7 or R there is very weak engagement, engine tone doesnt change much. Putting it mode and 1 doesnt change anything either so it seems like the converter or tcase is not transfering power. If I leave it idling for just another 5 minutes I'll get a very positive engagement and truck drives without issue. Anyone even seen that before? Fluid (15w40) is clear and full.

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[Ronmar]

Well thats weird. Any codes stored?

 

[GeneralDisorder]

Check the filters? Perhaps the fluid is too thick when cold and not flowing through clogged, collapsed, or damaged filter elements?

I would get the 15w40 out of it and put in Dexron ATF. The military stopped using 15w40 in the FMTV's and the ATF shifts better.

 

[Skyhawk13205]

Im not sure if this is a temp issue but recently since it's gotten into the 40's here when I first start the truck after a 5 min warmup the transmission is slipping and barely moves the truck, going from N to 7 or R there is very weak engagement, engine tone doesnt change much. Putting it mode and 1 doesnt change anything either so it seems like the converter or tcase is not transfering power. If I leave it idling for just another 5 minutes I'll get a very positive engagement and truck drives without issue. Anyone even seen that before? Fluid (15w40) is clear and full.

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Can you put into mode and check that range and select 1st gear. My guess are low pressure to your clutches caused by fluid restrictions. Allison recommends preheat for 15w-40 at 5deg F. You could also have a brake that are releasing slowly because of ice.