Lariatguy

Hey guys.. I have a 2008 f150.. 5.4 Triton. It's developed a loss of power since June. It does not have a rough idle... very smooth like always. It would cut out over 40 mph like a misfire. Only problem is that it does not do it all the time. I stopped driving it before I damaged anything. Just recently I was told to try high octane gas and some cleaner. Well that really helped it but not completely. It is a FFV and I had ran E85 in it the previous couple of months before the problem started. Should I change the fuel filter and keep running high octane to see if it will completely go away? Also I want to change the plugs. Any help is very much appreciated. Thank you