First i own a 2006 lbz with the ally 6 speed. is the 5 speed convertable into the six speed or is it a whole different trans. i ask cause i just picked up one at an auction that had a cracked bell housing but the tranny looks great inside my mechanic said it had abou 42000 on it. If not what about is the tranny worth in good running order without the bellhousing or torque converter. thanks jason

The five speed can be converted to a six speed with a pricey-- $$$ Southcoast valve body and a TCM. The original 5 speed has many different parts from the later Allison 6 speed and are not considered to be swapped without a lot of changes. :D

Many, many differences between 5 and 6 speed. Valve body, planetaries P2 and P3 have different helix angles on the gears, oil pump, entire rotating clutch assembly with FWD and OD clutches (C1 and C2), NSBU moved inside (IMS).