This is just due to the tranny/engine lugging until a higher RPM, less Torque is applied. The overdrive on these trucks are quite a reduction from 4th. When accelerating slowly, the TC should lock around 45-50mph and will probably "lug" under slow acceleration until a higher speed is maintained. If you accelerate at a faster rate, the TC will lock later, perhaps around 55mph (depending on a WOT or not). Since the engine is at a higher rpm and ground speed, it is easier to match the overdrive to the engine...IMO.

 

Good point for earlier trannys.... but this does not apply to the 47RE (introduced in 1997). It is locked in OD...full time!

RJ

 

thanks that some good info ill let him know!

 

What your describing sounds like "converter shudder" and this only happens when it just goes into overdrive. Once the rpm's go higher, the "shudder' goes away. This shudder indicate's your converter is on it's way south, if you tow heavy then that will finish breaking the converter.

I towed my boat down to the dealer and that's when my truck started shuddering. I took it in to the trans shop and had the converter replaced before it get's worse and takes out other parts in the trans.

 

Hmm, If I accelerate slow, after 4th my TC will lock around 45mph. If I accelerate at a much higher rate, lets say 3/4 throttle or WOT, my TC locks at like 55+mph. Unless my tranny is getting wore out or my TC is dieing?

 

'Dinner' - I don't know?
What you describe is same as mine...in 3rd gear. But mine and others I've driven are all locked immediately on engaging 4th (OD).
Was like this before the DTT also so can't be a stock thing??

Anyone else have a 47RE that unlocks in OD?

RJ

 

The earlier rigs have different programming. I've driven my buddies '99 and I don't recall it really being any different than mine though. Mine also locks in 4th right away.