TC unlocks at 50mph?

I had the same thing to my 2000 c5 might be the tcc actuator in the valve body
It won't set a MIL but it will get stored in the PCM.
The TC would lock and unlock at any speed over 67mph. The code P1810 also bumps line pressure, so you may be experiencing firmer part throttle shifts than normal.
It is a vig. 3200 stall. It all worked great before the h/c.

