is that slip with the tc locked?
Hopefully not, if the torque converter clutch slips, it wears just like a manual clutch would.
This is the chief failure mode of older 6L80 8L90s & 10L80s.
GM lets the clutch slip a wee lil bit to reduce NVH -
it also masks the uneven firing sensations when the engine pretends as a V7 V6 V5 V4 V3 V2 or I2 -
but eventually the worn out clutch takes out the rest of the transmission.
or do you need to unlock it while towing?
When towing (or hauling heavy), if the powertrain needs more RpMs and has to downshift to 4th or lower to cruise or accelerate,
locking the TCC would reduce powertrain cooling and reduce acceleration.
Primary purpose of locking the TCC is to improve MpGs at lighter loads and lower throttle angles.
The heavier the tow / haul, and/or the harder the powertrain has to work / play, the less time the TCC spends locked.
