When I go on/off throttle I can still feel drivetrain slack like something's moving. In certain conditions (cruise control especially) going down a hill I get vibrations while engine braking and the gear stick starts jumping around a bit on its own until it's out of that RPM range where it does that.

I've got z1 poly engine mounts, new Ebay rubber trans mount, Whiteline poly diff bushing. I took a video under my bumper yesterday and my subframe isn't moving around at all while this is happening, so it's not that.
How do I check my driveshaft center support bearing to see if that's the problem?
The two axle pieces on my diff wobble in all directions and seem pretty loose, I'm wondering if I could have a diff backlash/bearing problem given the PO ran it with blown bushings for god knows how long.

Should I just give up chasing this, as the car drives great otherwise and shifts perfect when I'm thrashing it. Just that occasional jerking and the fact I know something's wrong somewhere is driving me crazy, esp. given how much work I've put into it already.

Thoughts?

The cruise control in my 6mt will do the same thing when I'm going down a hill steep enough to maintain speed. I assumed it was just the computer not quite knowing what to do. Maybe try turning the two pieces of the driveshaft in opposite directions to see if there's any play?

I don't use CC enough to worry about it - but now you have me wondering again haha

Edit: I've installed subframe bushing collars since then, I'll see if it's still doing it, but I assume it will since they collars only made things stiffer.

Ok, that's good to know I'm not the only one with this problem. There's definitely play in my driveshaft and diff but I don't know how much is normal as I've only owned shitty old cars. I feel it when I'm not in cruise control as well, but it's harder to make happen if just driving normally. I can actually "play" with the slack a bit if I very slightly press the gas and the let off, I can feel it flex a bit, especially in lower gears going slowly. Although it's nowhere NEAR as bad as it was before I went and replaced all of the above.

Not sure how the G is setup with AWD, but on my Audi Quattro all you had to do was grab the drive shaft and it would wobble around if the bearing was shot. I had similar symptoms where it would feel like it was losing power, slow response, and going uphill the rear tire would like make a flopping noise. I ordered a used driveshaft off eBay, installed it, and those problems disappeared.