I agree with Brent. They needed to perform circuit pressure tests. These tests would indicate whether the oil pump is working correctly, stall test pressures in Reverse and Drive, engagement delays, etc.

Has this been a gradual symptom or has it happened all of a sudden? Anything else happen (no matter how small or insignificant)?

How does the fluid look? Smell? If you take the dipstick out, and place some oil on the back of your hand, does it look like there are a bunch of little black particles in it?