If sitting on the runway you can push your throttle to full, then hit the WEP button and it engages, your throttle is not the problem. Or for the picayune amongst us. Look up the rating for full throttle for your plane in Hg or inches or pounds or ata or Boost. Then watch your manifold gauge to see if it reaches that number when you push full throttle.
Over the years with different squads and missions this same phenomenon has been observed and become the source of jokes or heated concern. My squad regularly ups together, same fighter, same load out. We invariable have some players who pull ahead magically and we cannot determine how. I've watched the last squad mate in line when we are all in heavy P51D, same load out, same fuel. Gradually climb past the head of the pack and no one is using WEP or manual speed climb from the command line.
When I was in the old 56th we saw this all the time because we flew in groups with the same load outs and used WEP on takeoff for the first 7,000ft. We experienced the same phenomenon, usually with the same players pulling ahead in FSO because we flew in formation as part of the immersion factor.
Not all players connections are equal in this game. Anyone who has ever tried flying formations knows that.