I Have A 2001 Dodge Ram 2500 4x4 Quad Cab Diesel And I Only Have 75,000 Mile On It Im Still Pretty New To The Whole Diesel Engine ! Ihave Had My Truck For The Past 10 Months And I Love It But I Was Just Wonderign How Do I Tell If It Is A 2001 Or A 2001. 5? And Also I Ahve Done A Few Mods To It Such As Straight Piped It And I Have Added A Hypertech Tuner And I Was Wondering If Anyone Knows If It Is Stackable With Another Tuner And If So Any Suggestions Im Looking For Something Between 500-600$ And If Mine Aint Stackable I Can Sell It To Get A Better One. Also I Was Wondering If I Should Just Go With A K&n Or Maybe The Amsoil Filter For Better Air Flow And Witch One Is Better Out Of The Two? I Have Many ?'s But Ill Just Ask These Two For Now Thanks ?????? And I Love This Site I Was Reffered By Another Tdr Member Here In Tucson Arizona Thanks Roger