For the following reasons, TBMSport felt that it was necessary to rid the GMT360 platform of the 4 speed automatic transmission, known as the 4L65/4L70, with GM's latest and truly greatest 6 speed automatic transmission, the 6L80.
A) 4L65/70's just cannot repeatedly stand up to the power and weight of these vehicles under hard use. This will result in repeatedly rebuilding the transmission.
B) 4 speed autos drop the engine RPM out of its torque band during shifts, causing too much shock to the rear/tires and adding too much work load to the engine.
C) The new 6L80 comes from the factory behind engines making more power than TBSS and vehicles weighing more than TBSS
D) The 6L's are clutch trannys that automatically, with the computer control, adjust the clutches so you maintain the same consistent shifting as the clutches wears
E) For the most severe applications, the only upgrade necessary will be stronger clutch bands; which are available
F) The transmission swap cost is equal to or less than the cost of rebuilding the factory 4L60/70 and will last longer
G) Keeping current axle gear ratios will result in improved acceleration and fuel economy
H) Putting the 6L80 transmission in these trucks means less money in the long run with other mods, from forced induction to cam to exhaust. Do a transmission mod ONCE.
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