Looper or not

[wellcraftv20step]

I took the boat out again yesterday and had the same old problem, she would run great for the first couple of minutes then start to miss and bog rite down to where I cant get the rpm;s above 2000. Yhen while going along at 2000 rpm,s and the throttle in the wide open position she would just take off like a bat out of hell. It clearly seems like the longer I run it the worse the problem gets. Now it sounds like fuel but I took that tank out and flushed it my self 3x's just to be sure I was eliminating any bad fuel issues. And I took this boat out last week with no issues what so ever !! It ran really well, She has a new fuel pump ( VRO removed), New Timer base new Power packs; Carbs rebuilt, Wires. plugs. Seriously stumped here!!!