Do you have an EGR system? If so, it may be causing the truck to starve for fuel in an effort to lower emissions. Also, there is a history of the Idle Air Control (IAC) valve failing on V10s. Maybe yours is almost bad? Weak or dirty injectors... so many causes!

I had a '93 F150 that did as you describe. It would almost die at idle sometimes though. Anyway, I took it in to get it "fixed". Whatever they did to alter the idle made the truck lose some overall power. Looking back, I wish I'd just left it alone.