Second 2 stroke, first GasGas. Question

[JesseeS]

Hey all. Just picked up a 2011 GasGas ec300 six day?s with a rekluse clutch. I know it has an exhaust leak as it?s wet and jet black at the front of the bike and ordered new o rings and gaskets already. Also have some splooge out the exhaust.. When I took the bike for a rip I accelerated in first and it was steady from 1/8 to full throttle but not super quick, same in second, as soon as I shifted to third it was like a different bike. You could hear the tone change as if the bike said ?oh wait you wanted to go fast? Ok here we go?. My question is, is this normal? Or possibly a jetting issue? Perhaps the power valve? My only other 2 stroke experience is with a yz250 which was like a light switch in every gear. I?m just curious if this is normal for the bike. I know the bike is known for its ability to lug, which is what got me into the bike in the first place. If this is a stupid question I apologize, just trying to get used to the bike and learn it. Thanks for any help

Jessee