We are going to need to know if the truck is 2 or 4 wheel drive, it makes a big difference.
In need to get shifter off to remove transmission
If there is no drain plug you have to remove the pan.
They are inside of the transmission, Remove the trans. pan off the bottom of the transmission. And you will see them.
Check
The transmission fluid capacity of 2004 Chevrolet is 5 quarts. The fluid capacity needs to be checked before refilling in order to make sure there is no overfill as these are hard to remove.
Drain the radiator. Remove all of the hoses. Remove the transmission cooler lines if equipped with an automatic transmission. Remove the fan shroud. Remove the bolts that hold the top radiator support in place. Lift the radiator out.
You will have to remove the transmission. That is not a job for a novice. You need to take it to a repair shop and let them diagnosis and repair it.
Remove the bolts but be prepared for alot of transmission fluid pouring out. You will need a large drain pan.
It's between the engine and transmission. The only way to disconnect it from the crankshaft is to remove either the engine or transmission... or both.
You will need to go to a parts house and get the special tool that is required.
After you remove the Transmission oil pan. Just twist back and forth and push it out at the same time. I should come of.
Under the rubber boot covering the shifter, there should be 4? bolts. Make sure transmission is in neutral and remove these bolts, shifter should be able to be removed at this time