2001 Chevy Suburban water in floorboard

Water leaks are a little bit of a specialty. WE have a guy come in to do them and he also services all the dealers in the area.

What he does is remove all of the insulation/sound deadening material from under the carpet, pulls off interior trim to get a better look. ( That will need to be replaced as it will cause mold, odor and rot problems.) Then sprays down the truck in certain areas at a time and observes. Sometimes clues are seen once the panels are off

Keep in mind you want to simulate rain, not hurricane gale force winds by using a sprayer.

I would be most suspicious of areas around fixed windows first.