2002 express 2500 4.3 not shifting into overdrive

There is no codes but it will not shift into overdrive???fluid is good and clean and doesnt smell burnt and looks perfect

There is no codes but it will not shift into overdrive???fluid is good and clean and doesnt smell burnt and looks perfect
Should set a code.
Any check engine lights on or blinking?
Was it checked for codes with a transmission capable scanner or just a OBD 11 code check?

What transmission and what size van?

No check engine lights No codes I checked it with my scanner but I dont think its set up for transmissions.And its a 4160e 2002 chevrolet express 2500 with the 4.3

To get transmission codes and data you need a transmission capable high end/high dollar scanner.
Check some of your local repair shops or transmission shops.
If you can get codes post back code no.