I am not sure why some trucks have steel and some have aluminum. dmax's have had aluminum for years with no problems. lighter, no carrier bearing and strong.

 

How about this. Doesnt dodge carry 2 frame lengths? Ive got the longest one, because I have a 4-door long bed. Maybe the driveshaft depends on your frame?

 

Length of the shaft different on different models.
On the standard transmission, the length is different from the Automatic transmission if the model is same. Noe we got few different length models, therefore the drive shafts have different length.
I have the Megacab with Auto, and my drive shaft is aluminum and very thick in diameter. On my other truck it is standard, and it has a steel shaft.

 

that makes sense and ive got a reg cab therfore shorter driveshaft steel megas and quadlongbeds my have aluminum right?

 

It seems likely.