I think he is saying that the increased mass of the steel shaft's characteristics cause problems on drive trains that came with aluminum shafts.
I had a leak in my BURB from day one out of the rear of the transfer case. I put in a new from GM yoke, the bushing is tight, and replaced the seal numerous times. When I twisted my 3 1/2" .080 steel shaft, I went to a 4 1/2" .115 aluminum, and the seal hasn't leaked since. I truly believe these trucks need an aluminum ahaft as it also smoothed out my drivetrain in general TREMENDOUSLY. Having run both, the aluminum is hands down better in every way. You're already dealing with a drivetrain known to have problems breaking extension housings and bellhousings when driveshaft problems happen, why increase the mass and possibly make it worse.
