150cc gen 5 maddog wot issues

[Sammage]

Ok I know I'm not a complete dumb ass I been worken on mopeds for 9 yrs now granted all 50cc, had one bored out to an 80 for 5 yrs never had issues. Bit anyways long story short my bike use to hit 57, bogged once at wot so I changed carb adjusted valves changed fuel pump since most stock parts suck. Have literally done everything even tryed disconnecting auto accelerator. What it's doing thow is I can hit 50 for about a good 3 miles straight an then slowly loses power till its at 45 then runs fine I can rode like that for a few feet then wot at 50 for about another mile an back to slowly dien down. The bike has 10000 miles on it. Spark is amazing im just at a total loss an dont know if im missen anything. I have even checked all vacuum lines. No leaks. I'm hopen someone here can help me.