So my 99 has been running great in the snow we got a few days ago, other than those codes that came up for the 02 vendor. But the last few days I’ve noticed when it’s sitting all day while at work or when I leave in the morning, it don’t shift right. I get to about 40 mph and the rpms are receding up to 4 (you know what I mean). Then I’ll let off and start moving again and after a few times of doing this, it’s fine. It has been pretty cold in my area lately, could that have something to do with it? Maybe until it gets warmed up it will stick due to the cold? Once it gets going then, it’s perfect no rough shift or anything, very smooth. The fluid is full, so I hope this isn’t the start of the tranny going.

 

In order to get the engine + transmission at optimum temperature, the electronics keeps the overdrive unavailable. When it is cold, the driver sets the cabin temperature higher and robs the heat out of the coolant, thereby it takes longer to get to the optimum temperature .... so its takes longer to free up the overdrive.

It is recommended to keep the rpm below 3k till you reach optimum temp [temp gauge near mid point]. Some people let the engine warm up by long idling [not recommended] but that does not help transmission to get warm.

So drive slow till you reach optimum temp.

Salim
note: one my wild theories about transmission stress is folks driving at high speed before the vehicle is warmed up.

 

It's all about the emissions when cold.

Keeping lower gears longer forces the engine/exhaust to warm faster, and a warm cat is a happy cat.

Mew.

Oddly enough, my '08 LS 460 L doesn't do this. It shifts virtually the same way hot or cold.

Finally, an engine under even a light load warms much, much more quickly than does one idling, doing effectively nothing.