Deborah,
The tri-sensor is replaced by removing the two screws on the side of the TEE assembly. The Tri-sensor is inserted and sealed by compression and an o-ring. Once the screws are removed, you will most likely need some channel lock pliers to grab it. Twist back and forth while forcing it out of the TEE.
Make sure to add some lube on the oring when you put the new one in. Also, very important, make sure you align the direction of the flow paddle with the direction of the water flow.
You mentioned that you have 10 gpm? That sounds like either a pump failure, improperly positioned valves, or very dirty skimmer basket, pump basket, and/or filter. That doesn't sound like an AutoPilot related problem, but it sounds like the AutoPilot is shutting down the cell under the flow protection, as it should.
Let me know what you find.