It may have been sucking water into the air filter, a known problem with the earlier F53/V10 chassis. Ford issued a "snorkel" kit fix for the problem, but I don't think they're available any longer. I had a similar problem with our 2001 F53/V10 in a heavy rain. A quick air filter change and a let up in the rain got us to our destination with no further issues, but the filter I had removed was soaked. I cobbed up a 3" aluminum dryer hose extending from the bottom filter inlet to above the filter housing as a more permanent fix. Haven't had any problems in the two years and many wet miles since then.