What's your tap water pH?
Does the driftwood leach a LOT of tannins? (How dark/brown would you say the water turns?)
I don't know if Flourite leaches ammonia (which would be converted to nitrites). Try taking a separate glass/container of tap water and add the same layer thickness of Flourite to the container, wait a little while and then test that container's water to see if ammonia or nitrites levels rise.
You could do the same test with the driftwood. Was the driftwood collected yourself? (maybe it still had a lot of sap and/or microfauna that are now dying, creating sources of ammonia.
High nitrogen levels (in your case nitrites, but even the 5ppm ammonia was harmful) do harm/stunt/kill nitrifying bacteria. But it sounds like your ammonia-odizing bacteria (Nitrosomonas) are still present and doing their job. If you are getting increasing nitrates, then you do have some nitrite-oxidizing bacteria present (Nitrospira). Nitrite-oxidizers are slower to develop and do take longer to convert than Ammonia-oxidizers do. They just need more time to establish, but too high nitrite levels won't help.
So I would say to find the leaching ammonia source, then either remove it and cycle with the bottled ammonia, or just use the ammonia leaching source as the ammonia administer for the cycling process and don't dose bottled ammonia so nitrogen levels won't be excessively high.
Well, I had thought my tap water was 7.8 pH, but I just tested it (from multiple taps) and it's not less than 8.8 today, apparently. The tank is a solid 7.0, and has been since the ammonia dropped.
My driftwood (bought from LFS) leaches zero tannins. When I initially boiled it, that water turned to rust, but not even the water I used to soak it over the weekend had any coloration. The only visible affect the log has is developing a thin film of stuff that floats at the top of the tank. Not sure what it is, haven't tried to find out.
I'll test the Flourite for leaching, but I don't believe it does.
I guess on the assumption that there is an ammonia source, I'll leave the tank be and see if it doesn't recover on its own. Bah, I thought I was so close when the Ammonia dropped