I have a 06 Pontiac G6 3.5 with 241329 miles on it. When I start it up feels like it is missing or has a misfire. Today on my way home from work all of sudden it wouldn't shift into overdrive. Not the first time this has happen. So I pulled over and turn the car. After 5 minutes I turn the car back on the missing is still there but as I go to accelerate it goes into 1st and 2nd and 3rd. Shifts fine rpms are normal. Coming out of 3rd and into overdrive rpms drop to about 1k. It will pick up speed but you can tell the transmission wont let it go into overdrive. So i get home put the car in park. And put it in reverse then neutral then drive all shift fine while parked. I'm in drive while still park. And put it into the 3rd and it won't shift. So I put it back in park. And pull the gear shift into L and shift it into 3 and it does nothing. But if I put it in natural from Drive it will go.