01 Silverado- Shifting problems

My 01 Silverado has a significant shifting problem when it is cold outside. Problem is it won't shift up out of 2 until it has run for a good long time and by that I mean it needs to run at least 20 minutes. It comes down from 2 and back up very nicely and once it is completely warmed it shifts up very nicely from 2. I know basically it is designed to do this but I find it just takes too long. In town driving rpms are just too high to keep up with traffic. Engine warms up quickly, 4.8 with auto and mileage is about 75k. I'm thinking must be a sensor not working correctly. Any ideas out there? Thanks John

Mine does the same think but for only about 4 or 5 minutes...when was the last time you checked your trans fluid...maybe it's low.

A scanner will reveal the trans oil temperature sensor reading without so much as kneeling under the vehicle. If the trans oil temp sensor is reporting low, but still within the acceptable temperature range, the symptoms you report can occur. A poor connection in or outside the transmission, or excessive contamination can cause a low temperature indication. Speaking of contamination, you HAVE been changing the transmisison oil every 30,000 miles, right?

There may also be other problems, such as a 2nd accumulator piston or 2nd range servo sticking, blocked oil exhaust port in 4th servo, and others, but the fact that it seems to operate normally once it reaches operating temperature might point away from those possibilities. Besides, checking the temp sensor is easier.

A scanner will reveal the trans oil temperature sensor reading without so much as kneeling under the vehicle. If the trans oil temp sensor is reporting low, but still within the acceptable temperature range, the symptoms you report can occur. A poor connection in or outside the transmission, or excessive contamination can cause a low temperature indication. Speaking of contamination, you HAVE been changing the transmisison oil every 30,000 miles, right?

There may also be other problems, such as a 2nd accumulator piston or 2nd range servo sticking, blocked oil exhaust port in 4th servo, and others, but the fact that it seems to operate normally once it reaches operating temperature might point away from those possibilities. Besides, checking the temp sensor is easier.

Yeah...what he said...

I am going to do an oil and filter change and also get it scanned. An alternative to the oil change is the power flush that some service stations do now and I'm not that familiar with the procedure or how effective it is?? They flush all the oil including converter and only change the filter if they find a significant pressure drop. Price is about same. Thanks for info and I will keep posted on results.