The sound is the best way to tell is a DMF is on nits way out. Generally when they're starting to get loose they will exhibit a distinctive "clack, clack, clack" sound when you shut off the engine. What it is, is that the back half (Flywheel portion) of the DMF is getting sloppy and bouncing back and forth against the dampener springs when the engine stops abruptly. If you're hearing that, then now would be a good time to get it taken care of before it comes apart and wrecks the trans.
If the truck is more or less stock, you don't need to spend that much on a SMF conversion. A very nice LUK setup (which I highly recommend for a stock truck) will only run you about $275 on Rockauto. And it includes a new SMF, the disk, the throwout bearing, pilot bearing, pressure plate, and all the hardware. A great deal on a good clutch and as long as you're at or near stock power levels it will work really well.
More Information for LUK 07226
"Just a redneck geek"
1997 F-350 7.3 PSD, 4x4, CCLB SRW, 3.55's, ZF5
If it isn't under warranty, I'll fix it myself.