Not much can stir the pot like a good DFM debate. The DMF has had a bad rap since it hit the 7.3L trucks and we could discuss it here for a long time. You are not wrong for being concerned, but it will be tough to get data or autopsy reports on other installations.
Just curious, why are you replacing the trans? I do not know how you use the truck, competition, hot shot, daily driver etc.
1. The Ford 7.3L design has several features in it that the G56 DOES NOT have, like a torque limiting clutch pack. The typical 7.3L design can have over 120 parts down to the rivet.
2. Failure modes on the G56 DMF vs. the 7.3L design do not share very much in common, different designs and manufacturer.
3. DMF's are an advancement in Torsion Damper designs to further reduce engine created gear noise in the transmission.
4. The G56 went all the way in clutch complexity in my opinion. DMF, Self Adjusting Cover (SAC) and a torsion damper disc. About the only thing they left out is an internal slave cylinder.
5. Ford 7.3L up to '97 were all built with DMF's. In '99 when the truck was debuted as the Super Duty, they dropped the DMF in favor of a 13" solid F.W and a very large (but initially troublesome) dampened disc. For this entire series, the trans has been a ZF with alloy cases.
6. For the entire clutch aftermarket, one of our most popular sales has been DMF to Solid F/W clutch conversion systems. The sales are, well, very strong. IF conversions were impacting transmissions, the sales would not be there.
It is a subject of significant debate, but out powertrains were designed as a system and any change can impact the system, most all are considered positive, some have compromizes but what do you want your truck to do and how do you use it?