Sulfur Cube should never stop bouncing when filled with a slime block:

Imagine this, a Sulfur cube filled with a slime block to have infinite propulsion and infinite acceleration, kinda like something out of Meet The Cores 3, where the gels are mixed and a combo of infinite propulsion and acceleration are made in a deadly combo.

Considering that ice filled Sulfur Cubes that are on ice are already very slippery. I hope that the Sulfur Cube filled with a slime block will be extremely bouncy, like world height limit bouncy when mixed with a slime block placed on the ground.