4L80 shifting question

[dgrund61]

Need to know if my 98 6.5 is acting normal. At cruising speed the converter lock out ( I assume that's what it is ) kicks out when going down any down grade. When going on level or back up any gradient it will shift up or lock back up. This happens whether its in cruise or not. The rpm's only changes by about 100 so I'm thinking it's the lockup deal. I also assume that this is how the computer maintains the correct speed with the diesel. It not as noticeable at higher speeds such 65 to 70 , more so at 45 to 60. 160,000 on tranny and engine. Just had fluid flushed and new filter. Like I said just want to know if normal and if not what might cause it and remedies. Thanks

[JohnC]

4th gear has an over-run clutch that allows the engine to drop back to idle when you let off the throttle. Is this what you're seeing?

[dgrund61]

4th gear has an over-run clutch that allows the engine to drop back to idle when you let off the throttle. Is this what you're seeing?No, I only notice it when on slight downhill grades; as soon as you are on level or slight gradient it will shift up ( as I call it ) and drop about 100 rpm. It seems like it unlocks the torque converter to slow the speed down to maintain your speed, kinda like engine braking( if that makes any sense). I need to know if this is normal to the 6.5 or if there is a lock up sensor or solenoid that's acting up.

[DmaxMaverick]

Sounds normal by your description. Your model year would have the TCC unlock anytime with 0% acc. pedal or brake application. If the RPM is varying only 100 RPMs, I would suspect it is the TC unlocking/locking, normally.