04 grand prix chugging issue pls help

hi i have an 04 grand prix starting and driving around town like under 40mph the car runs great but when you get over 40 mph it will run fine for a min then it chugs then it runs good for a min then chugs etc. and sometimes it will like stay running but act like its dead it will idle at 1k rpm and wont let me give it gas and this is comming from anywhere from 40 to 70 mph so when it wont let me use the throttle it will just coast untill we come to a stop turn the key off and start it right back up then acts like nothings wrong again till we go above 40

It sounds like your car is either having problems breathing or getting the right sparks on time. Check the air intake system and/or spark plugs.