Car has misfiring issues after sparkplug and coils have been replaced

2008 Lincoln navigator. I had issues with
a newly rebuilt transmission. The guy
tells me to replace all spark plugs and
coils. I do that. It works for a little while.
Then misfired code started popping up.
Cylinder 6. We change injector. Checked
if spark plug sparks. Checked
compression in cylinder. Replace
injector. Ultimately the spark plug was
the problem. Replace it and it drives
great. 2 weeks after cylinder 5 misfire.
Change sparkplug. Not even 4 weeks in
and the new oem motorcraft sp is half
melted. Change injector also. Now the
codes are saying that cylinder 5.7.8.
Coils not working. I still kept old ones so
I replaced them. Also replaced 5678
cylinder spark plugs with E3 ones.
The car still misfiring.  I'm running out of
ideas. I checked the connections to
injectors and coils. They are secured
now with a small zip tie. The clamps
holding them in are missing. Still
misfiring.