I am on a cross country vacation right now not towing anything and have begun to notice that at hiway speeds going down large hills with Cruise control on it feels as if the the Torque converter unlocks and relocks as I coast. Is this normal and is that actually what is happening?

 

mine does nothing like that... are you in tow/haul mode? In TH mode, the tranny will downshift sooner and hold the gear longer. my TC locks & unlocks @ 28 mph...

 

Nope, not in tow haul. I have the 4 spd auto. It feels like the motor is missing or the TC is unlocking and relocking real quick down step grades in Cruise at hiway speeds.

 

Anyone else know what I am talking about? Anyone else have this experience or know exactly what is going on if thats not it?

 

if the TC was unlocking you would notice an increase in engine RPM's.

is the truck studdering/surging

 

Mine was down shifting in cruise as I ws going down hills to keep the speed at the setting and one time it hit second gear and woke me up.

So it will down shift out of OD in cruise to keep speed down

 

I might notice an increase in rpm's if I were on level terrain trying to keep speed, but going downhill trying to brush off speed or keep a steady speed downhill? I will continue to watch the tach when it happens and report back.

 

I've been wondering about how the lockup converter works as well. When I am driving, flat ground, or down a hill, and I have throttle on, cruising at say 55mph. The tach shows about 1500rpm's in overdrive. The second I let off the throttle, the engine rpm's will drop down to idle speed, while I am still traveling 55 mph. So I am thinking the converter is not locked up when throttle is off. Shouldn't it be? This is an 07 with a 5.9. Unless I downshift, there is no engine braking when in overdrive, is that correct?

 

Oh yeah, when this happens sometimes I just turn off cruise and foot pedal it down the hill and it doesn't do it unless in cruise....