Just noticed this the other day, when running around 50 - 55 MPH and the TC locked up when I let off the peddle my RPMs dont drop to idle and the TC stays engaged. Have to slow down to under 40 or accelerate to get the TC to disengage. The truck has just over 100K, I haven't been a heavy tower nor a racer, and I haven't seen any other signs of a failing trans. Temps seams to be normal, mid 100s when driving around town and 180 or so when running a little hard. Im not a big tranny tech, so Im a little in the dark here, so any help is greatly appreciated.
J

 

My dads 03 does the same thing but his may unlock at 45, cant remember, but i think its normal.

 

Normal operation, mine does the same thing.

 

I must be crazy to not have noticed this for the first 100K. Does yall RPMs stay around 1500(or what ever your RPM is) when you let off the peddle with the TC locked up because I can swear I havent seen it tell now.
J

 

What you are seeing is the TC unlocked...if it were to stay locked you would not notice a RPM drop when you let off the gas. Mine will stay at RPM until below 45 then unlock and fall to 1100-1400rpm's.

TC Locked= No rpm drop

TC Unlocked= rpm drop to near 1200 rpm's.

Hope this helps...I might have understood you backward but either way its probably normal.

 

Yep, done it for 110k miles. The standard programming holds the TC locked as long as possible.

Blip your throttle couple of times and you can tell the TC is locked.

 

The torque convertor is a fluid coupling between the engine and transmission. "Lockup" means a clutch engages and mechanically locks the engine to transmission for a 1:1 ratio. Lockup increases efficiency.

The 48RE goes into lockup around 47 MPH (no special modes selected), so at that point it will behave as a manual transmission does - RPM and speed drop are linked.

Lockup is also how auto transmissions can use an exhaust brake.

What you're experiencing is good, enjoy it.

 

Man thanks guys I must have been smoking some good stuff earlier this week I guess that I must be on the defense ever since my truck rolled over 100K and start second guessing everything, I have just never had a truck that has been this worry free. Thanks for the reassurance.
J