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Hi I have a 1988 7.3L and am a bit confused. from what i can tell i have the C-6 Trans without overdrive. I drive a lot of highway miles and would love for my rpm's to drop a bit. is there any way to swap out to a c-6 with overdrive or another trans and if so how do i add the extra gear spot on my column shifter???

Colorado 7.3
 

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how do i add the extra gear spot on my column shifter???
I don't think you do.... I think it's just a lock-up torque converter (which can only be put onto a trans made for it). This is considered O/D. At least on some transmissions.... I dunno if this applies to the C6 or not though. If you did get one with a lock-up torque converter, you'd need the electronic controller to lock it and unlock it.
 

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you could get a Gear Vendors overdrive/underdrive kit. it goes behind the tranny and ultimately gives you six gears instead of the 3 you have now. an od tranny isn't one with a lockin TC though it does have that. it has a additional gear that has a ratio of less than 1:1. in example my E4OD has an overdrive gear of .71:1.

the c6's final drive gear is a 1:1 ratio. it gives you a final drive ratio of whatever gearing you have in the rear end.

with the gear vendors unit it drop your 1:1 ratio to a .78:1 overdrive. they run a little on the expensive side but not more than you would spend on switching trannies. and you'd have the reliability of the c6 and the extra gearing you need.
 
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