O/D off
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Joined: Jan 2011
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From: Zephyrhills,Fl
.You'll notice a difference with it on or off...the sound of the engine, I know at mine at 50 MPH it feels like I am at the top of 3rd gear...If I know I'm not gonna be going over 45 or 50 MPH, I will just turn mine off.
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Joined: Apr 2010
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From: Clayton MI
If I am not towing/hauling anything, I leave it on, and let the trans decide what it wants to do...... I live in a fairly rural area though.... so, speed limits over 45 are pretty close.
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Joined: Jul 2006
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From: Gainesville, Ga.
when the light if on, then the OD is off, and your transmission will shift one less time, and you'll have more pulling power at that in-between speed of 45-55.
when the light is off, then the transmission will shift one more time into overdrive. this will provide better MPG and lower engine RPM, but less pulling power. i'm not sure about your 94, but it might shift into OD at somewhere in the 45-55 mph range. if you have a tach, you'll notice about a 500 rpm drop. to further confuse the issue, you will also feel/see what looks like another shift, but its not - its the torque converter clutch lockup. on my 01, this is another 300 rpm drop on the tach.
again i don't know about your 94, but on my 01 46RE, depending on pcm software version, the TCC lockup can still occur with OD off (or not).
in general -
if you are towing or heavily loaded - turn OD off.
if you are driving in town at 45-50 and the truck feels sluggish, or is shifting in/out of OD a lot - turn OD off.
if you are on the highway running 55+ (and not towing), turn OD on.
when the light is off, then the transmission will shift one more time into overdrive. this will provide better MPG and lower engine RPM, but less pulling power. i'm not sure about your 94, but it might shift into OD at somewhere in the 45-55 mph range. if you have a tach, you'll notice about a 500 rpm drop. to further confuse the issue, you will also feel/see what looks like another shift, but its not - its the torque converter clutch lockup. on my 01, this is another 300 rpm drop on the tach.
again i don't know about your 94, but on my 01 46RE, depending on pcm software version, the TCC lockup can still occur with OD off (or not).
in general -
if you are towing or heavily loaded - turn OD off.
if you are driving in town at 45-50 and the truck feels sluggish, or is shifting in/out of OD a lot - turn OD off.
if you are on the highway running 55+ (and not towing), turn OD on.
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Joined: Sep 2013
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Default O/D to off
Is there a way to default to O/D off?
when the light if on, then the OD is off, and your transmission will shift one less time, and you'll have more pulling power at that in-between speed of 45-55.
when the light is off, then the transmission will shift one more time into overdrive. this will provide better MPG and lower engine RPM, but less pulling power. i'm not sure about your 94, but it might shift into OD at somewhere in the 45-55 mph range. if you have a tach, you'll notice about a 500 rpm drop. to further confuse the issue, you will also feel/see what looks like another shift, but its not - its the torque converter clutch lockup. on my 01, this is another 300 rpm drop on the tach.
again i don't know about your 94, but on my 01 46RE, depending on pcm software version, the TCC lockup can still occur with OD off (or not).
in general -
if you are towing or heavily loaded - turn OD off.
if you are driving in town at 45-50 and the truck feels sluggish, or is shifting in/out of OD a lot - turn OD off.
if you are on the highway running 55+ (and not towing), turn OD on.
when the light is off, then the transmission will shift one more time into overdrive. this will provide better MPG and lower engine RPM, but less pulling power. i'm not sure about your 94, but it might shift into OD at somewhere in the 45-55 mph range. if you have a tach, you'll notice about a 500 rpm drop. to further confuse the issue, you will also feel/see what looks like another shift, but its not - its the torque converter clutch lockup. on my 01, this is another 300 rpm drop on the tach.
again i don't know about your 94, but on my 01 46RE, depending on pcm software version, the TCC lockup can still occur with OD off (or not).
in general -
if you are towing or heavily loaded - turn OD off.
if you are driving in town at 45-50 and the truck feels sluggish, or is shifting in/out of OD a lot - turn OD off.
if you are on the highway running 55+ (and not towing), turn OD on.
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Joined: Apr 2010
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Likes: 4,211
From: Clayton MI
Yup. There is even a write-up for it in the DIY/FAQ section here. O/D off switch is just a momentary switch, that sends a signal to the PCM. Using a relay triggered by the ignition switch in the start position will send the signal. O/D defaults to off. 
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Joined: Apr 2010
Posts: 87,387
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From: Clayton MI
Yeah, don't use O/D when towing any significant weight. If it's just a little camper, or small trailer with your lawn tractor on it, should be ok, but, anything beyond that, push the button. 