Carbon buildup is a huge problem on 4.7's and 3.7's and more times than not a decarb doesnt work. Honestly you may be looking at headwork here... I question the leakdown test as I have had a 2 4.7l's and 1 3.7l that had good leakdown after about 65psi when the pressure in the cylinder clearly seated the valve and leakdown dropped to almost nothing but before about 65psi I had nearly 50% leakage... in this case the fact that there is almost no leakage at 100psi doesnt mean anything because your volumetric effiency is down, at a low warm idle is when this will cause the most problems because the speed of the engine is slow enough that the leakage is magnified, instead of spinning so fast that it builds enough pressure to seal the cylinder quickly it will allow oxygen to escape causing a poor air/fuel mixture. The fact that you have a low engine speed misfire leads me to believe it is a volumetric effiency issue.
Ultimately the 3 mentioned cars got reman cylinder heads, 2 being warranty and 1 being a car for the sales department
. I put new valves in 1, swapped lifters, rockers, plugs, coils, and injectors to no avail, I am not sure if it was a valve seat falling out that I didnt catch while I had the valve out, or if there was a valve guide concern, honestly I am not sure the exact cause myself, all of that to say I have seen something nearly identical a couple times and it took a cylinder head to repair the concern... you may be lucky and get a machine shop to pinpoint a failure for you if your not ready to buy reman heads.