Sounds like a bad timing chain tensioner. (The "popping" noise is the timing chain slapping around) Does your scanner have live data? If it does, pay attention to the cam timing or VCT when it starts to misfire/pop and see if the timing advances or retards. I had a very similar issue on my 06' 5.4 and it was the timing tensioner. On my Edge I would watch the cam timing and it would be around 40-45* then once it started misfiring/popping it would drop to 0-2*. Mine would idle fine, rev up fine, and drive fine through 1-2 gear but once I got above 45-50 mph and around 1,700-2,800 rpms it would start misfiring/popping anytime I'd try and slightly accelerate through that rpm range.