Hey guys I have been struggling to get my TCC to lock up consistently and need your help. The issue is at steady speed once the TCC is set to engage in the tune, it locks, then unlocks sort of a hysteresis deal. It will randomly hold for X secs and then it always unlocks Y secs later. It will not hold for longer then 5-10 secs max. I've datalogged the heck outta this issue and I think the issue is that my RPM / Tach input looks sort of a saw-tooth pattern (200-300 rpm swing), which is why I think it unlocks/locks ("Negative slip prevented TCC Lock").

I've gone back and forth with TCC problem and Engine misfires as my working theory and I'm now at the end of my rope and need your help.


The setup:

-Carb'd BBC with MSD 8365 HEI
-Using 7060 PCM to control 4L80E: Hooking MSD conditioned tach output (gray wire) to feed 7060 PCM + factory tach (purple/white wire for trans control {CKT 430, PCM Input D14, EST Reference} and white {tach lead} wire for dash tach is hooked to gray MSD tach wire). The 7060 controls the shift points perfectly.
-Carb TPS adapter.
-4l80E with PTC Torque Converter



Attempted fixes:

-New Plug wires, Distro, Plugs (Plugs look good)
-Changed curve with different HEI springs
-Locked Timing
-New upgraded Triple Disc Torque Converter
-HD2 Transgo shift kit installed
-Burned new chip to have TCC engaged at 60, 70 and 80 MPH w/no change. Also upped TCC Max/Min duty Cycle to 98% min and 99% max (I even hacked the XDF to add Max Duty Cycle in 7060).
-Tried to hook gray MSD tach wire up ONLY to purple/white 7060 PCM input to see if maybe sharing the output was the issue.
-Verified Distro End play is w/in spec: .012

Temp fixes, these have fixed the issue for a very short time:

-Changed to "large" silver springs so the advance comes on late (3500RPM is full timing) & changed plugs.
-Locked timing- this worked until I added an efan (????)


The truck runs and drives fine, so I'm thinking there may be an issue with the tach output of the MSD (?). The weird part is my tach gauge looks completely fine crusing down the road, but the 7060 PCM somehow pics up a 200-300 delta in the RPMs at steady cruise, this is really weird since both are hooked to the same source (??). Maybe the dash tach doesn't have the same resolution as the PCM?

My question for you guys is in the 7060 and/or 7427 PCMs is there a way to "Force lock" the TCC so it's only inputs for lockup logic would be MPH & Brake pedal (and disregard the erratic / saw tooth RPM)? Sort of like a manual switch to lock TCC based of MPH. I realize this is a bandaid-type fix, but I've thrown enough $ at this already with no results. I really want to steer clear of the physical TCC Lockup switch, which introduces human error like forgetting to switch it off when coming to a stop.

I know this is sort of an out-of-the-box question, but if anyone has any inputs they are greatly appreciated!

Thanks!