Torque Converter unlocking when load decreases

[79Firebird_99TA]

So I just got my TA back from an engine rebuild. Now the TCC unlock isn't right.

It's not in the tune, so that can be ruled out. I can't imagine what could have happened to it. I suppose it's possible that the TCC or lock solenoid is gone?

For example, I'm driving 70 on the highway and it's loaded going up a hill, it's fine. Once I let of of the accelerator very slightly, the TCC unlocks and revs up as I accelerate - then locks. Any suspects as to what is going on? I'm getting around 10-12 MPG like this.

[79Firebird_99TA]

Oh ... also I'm on an SD tune - not sure that it matters. Load would be measured from the MAP sensor. If anyone has any troubleshooting tips, I'm all ears. There are a few TCC channels in HP tuners that I enabled the last time I logged it, but haven't looked at it yet.