Yes it is. I get stuck driving a Silverado some times and it is the same way, full of water every time it rains.
I have to back it down my lane into the woods to get it on a hill steep enough to drain the 3” of water in the front of the bed. Then set there several min for it to drain.
Chevy trucks are worthless crap.
NOBODY , but NOBODY buys plastic bedliners... they trap water between themselves and the bed causing major rust issues ... for at least the last 10-15 years the only way to go has been to do the heavy spray in protection coating. http://www.linex.com/pages/2010/bedliners/index.php