Generally speaking; axle-hop is caused by the spring being wrapped up into an S shape, the tires begin to slip, and then the springs unwind and the tires catch.. This repeats over and over until you back off the throttle to stop the spring flex; or increase the throttle to keep the tires spinning.
Mopar figured this out decades ago and to help prevent this she moved the rear end forward on the springs and stiffened that front portion. Of course this bias makes it worse in reverse.........
Practically; if the springs are not strong enough or not clamped, then anything that fluctuates the power application can cause the springs to Wrap up/unload. Things like an engine/transmission moving around on the mounts or the clutch being modulated not by your foot.
In the forward direction, the snubber is your first line of defense, as it wraps up and hits the floor pan, and power application keeps it there. However, in reverse it goes the opposite way and is no help at all. In reverse you only have two ways of controlling wrap up; namely the ability of the springs to resist it, and the shocks. So de-cambered,unclamped, soft, 6-cylinder springs, with worn out shocks, are the worst at controlling this.
While clamped,SS springs,with properly working shackle angles, and long shocks would probabbly be the best.
You're talking on the street right?
Put the trans back down on the mount. Up in the air it's like on a jello stick. The X-member is tight to the frame,right?
What snubber are you running?
Are the axle tubes properly welded to the perches?
How high is the rear jacked up? or
Are your spring packs flat with little to no arch? How many leafs per side and how many broken ones? Are the shackles set in the proper working angle window? Are the Front eye-bolts tight in the bushings and properly fitting the perches? Did you cut any of the spring clamps off?
Are you running the correct length rear shocks, not at one end of their working range?
8.75 rear? with a SureGrip?
The pinion angle you set has nothing whatever to do with controlling axle-hop. That pinion angle is strictly chosen to approximate some minimum working angle under full power that will; A) NEVER go nose up, and B) approximately equal the front angle but in revese phase. This is strictly to prevent parts breakage, and to help transmit maximum power in a straight line WOT situation.
For a streeter, if forced to, I recommend to bias towards cruising vibration free, making the angles closer to the same but oppositely phased and ALWAYS nose-down at the rear.
BTW; nose down at the rear means; pinion nose down, relative to the driveshaft. In elevation view, at the rear U-joint, this will always look like a shallow V.
At the front, the working angle can be as little as 1.5 degrees, which keeps the grease working around enough to keep the needles from digging grooves in the cross-pins. With slantys,1* seems to be enough.
At the back, up to 7* might be required to prevent nose-up with some hi-powered/ softly sprung combo. Typically 3 or 4 degrees is enough.
The more I think about your description, the more I imagine the shackles making trouble. Check their working angles in reverse compared to in forward. If they are flipping over-center, they could be the combination of "clunk" and "hop".
