Driveshaft slip joint rotational play?

How much play should there be between these two parts of the driveshaft? I have a humming noise at highway speeds plus slight deceleration vibe. The U joints all seem solid but the slip joint rotates about a 1/16" back and forth. The rear axle bearings are good, I changed the rear, front, and transfer case fluids and all looked good and clear yet. The weird thing is the noise is most noticeable above 40mph to 75mph but goes away completely at 85. I swapped a set of different tires from a buddies Tacoma to rule out tire noise. Noise and vibes are there in 2wd and 4wd