I just recently purchased a 08 outlook xe with 57000 miles on it on July 8 2013. 2 days after I signed papers on it, my wife was driving it and told me that the car was acting funny. Said it was shaking real hard, real hesitant and rpms were running higher then usual. She pulled off the interstate because she thought she had a flat it was shaking so hard. Once she started driving again it ran fine. Thought maybe she had hit the shifter and had it in wrong gear. Couple days later I was in the vehicle with her and it did it again. The rpms went from about 15000 to around 45000, car started shaking violently, heard a popping sound coming from what sounded like the tailpipe from inside the car. Then all of a sudden load pop sound and car straightened up and drove like a dream. No warning at all. It's like a light switch flipped. I realized the Trans was slipping and making it act this way. I had only had possession of the vehicle about 25-28 days at this point so I contacted the gm dealer I purchased it from. They told me to bring it in for diagnostics. They told me couple days later that it was the 35r waveplate and order a re cert Trans to install. Said good deal. Trans had a used case but brand new guts in it. Along with trans they replaced the trans control module also. They called me a few days later and sad it was ready to come get it. I did. It drove excellent for approximately 2-3 days. Wife then told me it was doin the exact same thin g again. I carried it back to dealer. Told them something wasn't right, still having same problem. Me and Trans tech drove it around a good while and had no luck getting it to duplicate issue. Hooked scan tool to it ...... Nothing showing in the computer. Not even under history. Said ok. Drove it home. This happened off and on for several days, every time my wife was driving. Finally about a week and a half after I picked it up from getting new Trans , it acted up again when I was in the car. (Saturday august 17) Again, rpms shot up, hesitatant not wanting to accelerate, popping sound from tailpipe, and violent shaking in whole car. I manually shifted the shift lever to low. Trans automatically shifted down to 4 th gear like it was suppose to, I the tried to shift manually into 5th. Showed 5 th on the dic but felt nothing in the Trans to even insinuate it tried to shift. Tried 6 th. nothing. Did this several times. No luck. Shifted back to overdrive and after bout 10 minutes straightened up and ran fine. First thing Monday (August 19) I carried back to dealership. Said no go. Still acting up. Gave me a loaner and drove it till Wednesday the 21. Never could get it to duplicate the problem. Dealership then got gm technical assistance involved seeing the Trans checked out to still be good and couldn't quite figure out the problem. Gm said fuel pump. Order fuel pump and put it in. Was told Friday August 23 car was fixed to come get it. Was told that wasn't sure if fuel pump would fix it or not and if the problem persisted then we would do a swap out. Drove car all weekend then sure as anything Monday the 26th acted up again. My wife recorded the behavior on her phone. Did same stuff as before only this time dash lights were flashing like crazy. Took it straight back to dealer. Told them no go yet again. Said I was done messing with it and wanted to swap out. Showed them the video of car, and all of a sudden they new what the problem was. Loose ground they said. Checked ground under hood. Tight. Checked ground on battery. Said it was loose. Well I have a little knowledge of mechanics. I have a vocational associated degree in automotive and diesel mechanics. Work in industrial maintanence at local steel mill. I checked the cable and other then a little corrosion nothing seemed to be wrong. Was told it was loose ground causing it to do this. I disagree strongly. Well now I am being offered a 2 year 24000 mile bumper to bumper extended warranty that covers everything to keep the vehicle. After I was told if it came back after fuel pump I would be swapped out. Now being told if it does it again after the battery cable change, THEN I would be swapped out. Only reason I am getting all the help I am getting from the dealer is I have family that works there. I don't mind taking the warranty and keeping vehicle if I was 110% positive the original issue was fixed. I don't believe it is and don't want to waste anymore time and money on the car, I.e. car payments. ( car has been at dealership 21 days out of the past month and a half ) it is there now. Just curious if anyone has any idea what is wrong with this thing. Or any reassurance it is something as simple as a negative battery cable. Which I highly doubt. I think it is part of the problem, I.e dash lights flashing but not the whole problem. Several ase certified master technician buddies of mine agree. Any help would be greatly appreciated on this. Or if gm would step in with any advice that would be greatly appreciated also. Thanks in advance and apologize for lengthy post.