Driver side rear water leak

[Ohio04LLY]

Hey guys,

 

I have a 2004 Silverado 2500hd crew cab LT3 that currently has a water leak on the driver side rear. I have noticed an increased amount of water in the sliding rear window track as well as under the driver side rear door sill plate after it rains. I replaced the cab vents, the rear window, and the 3rd brake light  around a year ago.  The window has recently begun leaking again but the third brake light as well as the cab vents appear to be sealed. What could be the cause of the water pooling in the rear drivers side corner of the cab under the trim? Truck does not have a sunroof or cab lights. Any help is appreciated.