I am about to buy a Dodge Ram3500 , 5.9 HO ,48RE tranny
and would like to install Banks exhaust brakes and was told that the automatic Transmission was not capable of handling it, Could somebody explain to me why and is there other alternative, Thank you

 

Should work, works fine in my Auto but I had to add a Smart Control to keep it locked up, but the newer trucks allready have that feature I believe.
Adding the Pac-Brake to my truck was one of the great additions, it really helps hold my 5er back on the mountains.

 

Welcome to the site Pura Vida,
Look HERE for a post relating to the Jacobs exhuast brake. I think they also have a statement on their web site. However, I'm not sure about the other brand manufacturers. I think that it was not recomended for the previous stock automatics, because even if you could lock up the stock torque convertor, the rest of the transmission would not stand up to the task for long.
Most folks that run an exhaust brake like Chuck, have upgraded trannys in order to do this. You might try searching through the 3rd Gen-Engine and Drivetrain forums for more information concerning this.