T-bars vs Stored energy

Ok, the basic problem you're having is uncommon to Mopars, but very common to GM cars with trailing link rear ends...so perhaps looking at what causes those cars to hop might shed some light on what's happening with yours.
On those cars, the upper links face away ..upward, from the lower links. In four link terms, the Instant Center is out to infinity and so the rear never has that levering down effect that keeps the tire planted. Ideally, the point that those two lines would intersect would be right about the top of the trans tunnel.
Generally speaking, the point where the pinion snubber allows the snout of the rear to rise to, and the forward spring eye form that imaginary geometric triangle that would be the Instant Center of a Leaf Spring car.
Soooo, follow along. If you were to draw a straight line from the axle centerline, through the rear U Joint and then forward to the firewall of the car, and then draw a second line from Locating Pin of the Leaf Spring forward through the forward Eye bolt of the Leaf, where exactly would those two lines intersect eachother?
I would plot that out with the car at rest, and also do it with the pinion in its upward, "loaded" position. If either of those illustrations show the Instant Center out to infinity, that's where I would look for the problem.