Pontiac g8 gt shift problems

[455_PWR]

My g8 has been having wierd shifting issues, and I want to see if anyone else has shared these experiences or has a clue as to what the issue is. It should be noted the car is bone stock except for a corsa cat back exhaust system.

The car has 26k miles and drove great with no problems. Earlier in summer I was on the highway (cruise set somewhere around 60mph). All of a sudden the car jerked, the rpms rose, the cruise shut off, and the check engine light turned on-then off immediately. I let the car coast and the rpms lowered and the car up-shifted. It happened three times on that week-long trip. Today I went for a ride around town (40-ish mph), and it is happening every mile or so with no cruise on (car jerk, downshift, check engine light flash on/then off, then the car shifting up and returning to normal.

It does not have any issues in manual shift.

I have an extended warranty through Ford till 2014 or 100k miles, but I hate letting other people drive/work on my car. Has this happened to anyone else, or anyone have any clues as to the issue may be?

I am hoping it is electrical and not the transmission going... esp since the car has not been beat on!

Thanks