Strange Torque Converter ???

[buzzfx4]

So, I had something strange happen to me today with my torque converter. I'm not sure if its normal and I have never noticed it or there something wrong with the torque converter or the programer is telling the computer something fun.

I was driving through the northern lower Michigan where there are some good long 25-35% grade hills. I was traveling around 60mph and the programer with custom tunes was showing that it was in high gear and the converter was locked up. While going down some of these steep hills I would let off the gas so note to pick up to much speed. While costing down the hill the converter would unlock the second I let of the gas but about half way down the hill the programer would show that the convert re-lucked up, which you could feel. The funny thing is, that when it re-lucked up, the truck would be still in 4th gear and the truck would start to slow down though what I feel as engine braking....

I'm not sure if this a normal thing, (but I never really felt it like today) or there is something wrong computer/electrical or mechanically.

Thanks for any insight