I was monitoring some Torque converter params for my 4R55E with my in dash scantool.

For example, in park, it will say Desired Slip 1200, Actual: 730 (guess the engine rpm)

As speed increases, the Desired Slip drops (don't remember exact numbers) as well as the actual.

At highway speed, when it should be locked the Desired Slip says 0, but the Actual varies between 2-6 RPM.

Does this mean the torque converter is slipping bit? Seems it should be locked at zero in overdrive at 60Mph.

 

That could be within the margin of error for the sensor. I wouldn't worry about it, but I'm not familiar with your specific transmission.