sounds like ur getting rid of more oil than u think u are. my car does the exact same thing, since it burns oil. it runs really great for the first two weeks, but when i start dogging it about the 3rd week, when it really gets goin, it hesitates to get higher rpms. it feels like it MISFIRES and then it kicks in again. if you dont watch ur oil level, this can happen!

what ended up happening the first time was my engine could not rev over 6500 rpms and the check engine came on. i even took it to a shop and they couldnt figure it out. i thot i had checked everything, but sooner or later i found out my engine was too low on oil! ur engine has to be well lubed to be dogged most of the time! i say just take it easy with ur car till u get the oil problem fixed. otherwise, ur just begging for a new engine!