My 2001 f 150 truck shuts off when put in drive or reverse..

most likely the tranny filter has dropped in to the pan,drop pan,if so this creates a pressure differential in the valve body where it shouldnt,common in older fords,will affect both forward and reverse,usually reverse first.

is it a ford or chevy? could be vac leak or idle control

That's the reason i gave it up!! Well part of it.

IAC valve stuck open. very common!! you can try tapping on the IAC with wrench or something while truck is at idle. have someone put thetruck into gear. if it stays running,the IAC was stuck. replace it. easy fix. alot easier than torque converter