Hot Transmission

I have a 2004 Chevy Silverado 1500. We replaced the transmission just over 6 months ago and now the message reader keeps telling me Hot Transmission. I checked the fluid and its good. What else could this be???

Perhaps your transmission cooler that runs through the radiator is bad.

If not the cooler maybe there’s a problem with the transmission slipping or the wrong fluid.

Much could depend on the transmission you installed; used, reman, rebuilt, rebuilt properly, etc, etc.
Who done it?

I believe it is a used one. My cousin took it to a mechanic he knows. The used transmission only had a 30 day warranty. Should I take it back to the mechanic shop and have them look at it?

You should take it to an actual transmission shop - local, independent - and have them look at it.

Get somebody with a scanner to scan the computer. Also check the actual temperature of the fluid and compare it with the temperature reading on the scanner.