Overdrive

I have noticed in the winter months that my overdrive acts a little funny. The truck will shift into overdrive but still run about 2000rpm at 55 to 60mph. After the temp guage holds steady(about 10 minutes of driving) it will run about 1500rpm at the same speed. The truck is an 01 Z71 and has 77000miles on it. So is this normal or is something going out.

P.S. The truck shifts very smooth

I have noticed in the winter months that my overdrive acts a little funny. The truck will shift into overdrive but still run about 2000rpm at 55 to 60mph. After the temp guage holds steady(about 10 minutes of driving) it will run about 1500rpm at the same speed. The truck is an 01 Z71 and has 77000miles on it. So is this normal or is something going out.

P.S. The truck shifts very smooth

What may be happening is you are feeling the trans go into 4th gear, but not getting the TCC to engage until the engine starts geting close to operating temperature.
I wouldn't worry too much

mine does the same thing...even a friend of mine's f-250 does that. My old chevy had a sensor onthe exhaust manifold that senses the temperature and then it would allow it to shift into Overdrive. I assume that is to ensure proper power. Engine doesnt run as it should until the correct temperature is reached.