I almost have a similar problem but not at idle. Mine under load in overdrive will start bucking when you start to gradually give it fuel before it wants to drop down. Never throws any codes. If i hold it steady i can get it to keep doing it, With stock tune i hardly get it happening maybe feel it very mildly, sct x4 50hp tune it does it fairly often pretty bad, higher hp tune even worse. Ford thinks its ipr acting up and tunes are affecting it making symptoms worse. Truck idles great, just bucking under load over 50mph, worse on hills. Great fuel pressure 65idles lowest ive ever seen was 55, usually 58, has newer fhcm and tank cleaned and sumped, New ebp, icp, injectors, ficm, glowplugs, glowplug module, tranny has 10k, motor has 40k studded deleted, kdd heads, new hpop, oil cooler, turbo replaced and cleaned all parts motocraft including filters, rotella t6 5w40syn 6k intervals with archoil every change, and stanadyne everyfill up, fords new yellow elc (not gold). I gave up diagnosing it, ive literally changed everything on truck i feel like lol, and seemed like classic injector symptoms to me but they assure me its not. Ford claims the ipr is acting up, and the increased oil pressure demand from tunes is making it act up worse, no pids are jumping out on ae or ids as out of spec, passed buzz test and multiple contribution tests, and compression. Only thing they could say was ipr and icp desired vs actual was slightly off at the rpm and speed im having the issue, and the psi is jumping up more than it should be at that rpm range , but they claim normally it wouldnt be enough for concern, but i had them try with the tune and it was worse, but still not alarming according to tech, but its the only thing thats basically isnt perfectly ideal. I thought ipr usually would show up at idle or starting issues, i have none of that, only what feels like an injector issue under load, he claims he's had trucks with no classic ipr symptoms running poorly or do strange things like mine run like a different truck after swapping. Im going to change the ipr per there recomendation, and only reason its basically the only thing that hasnt been replaced yet, is it was lower mile one i replaced 70k miles ago before rebuild. We will see.