Dodge started the 6 spd somewhere around the end of '99. It was only put in a small # of trucks, due to reliability and prodution issues. When the HO cummins came out, (2000?), it was only available with the HO (as far as diesels, dunno about gas), and the HO was only available with the 6 spd.
I saw somebody advertising a conversion to the 6 spd from the 4500, was pricey, don't remember who (standard trans, maybe?).
Pete
'83 K5, 350 TBI (ex 6.2), 700R4, NP208, Dana 60/14 bolt, 4.56s, Detroits, 3" lift, 15-39.5x15 TSLs
'97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd