Has it always did this or only recently? Does it only do it at light throttle or also at WOT? If it does this all the time, you could have a damaged release side servo o-ring or the wrong ring. If it only does it at light throttle, you might need to raise TV pressure (longer mod. pin or screw in on the mod. adjusting screw). But again, if it's doing it at full throttle, you'll likely need to disassemble and go through it.
Ken Collins, BadShoe Productions, How To DVD's specializing in Ford drivetrains www.badshoeproductions.com (banner ad below)