I have a 2007 GP (base model) I purchased used in September of 2012 with around 127,000 miles on it. To date I have a little over 140,000. When I first purchased the vehicle, there were absolutely no issues with driving that I noticed and I am very sensitive to how cars handle due to my POS '05 Grand Am that turned into a money pit. Before purchasing the GP I had a local shop check it all out and all that was noted was a slightly loose outer passenger tie-rod that I negotiated into the price. After a week or so I brought the car to Belletire and had the tie rod replaced. After that I can't recall any difference in handling, which is good. Skipping a few months of good handling I had a few minor things here and there done like plugs/wires replaced just as a tune-up. I also decided to do a few routine GM recommended maintenances, such as Fuel System cleaning (helped with somewhat rough idle), Coolant flush, and lastly a Tranny flush (worst idea ever). Not too long after I started to get this harsh shifting which was later diagnosed as the popular P1811 code common in the 4T65E trannys. I've had it back to the dealer twice now because they told me a flush wouldn't harm in anyway and all they do is clear the code which allows the vehicle to shift smoothly for a couple days. Another issue along with the hard shifting I have noticed is this really annoying vibration. I have done quite a few things to the vehicle to try and get rid of the vibration, and nothing really seems to work. The vibration is felt in the seats as well as the steering wheel and seems to get a little bit worse upon acceleration. If I grip the steering wheel at the time and drive down a road going 50-60MPH, my hand moves left to right a little. This is where I need some input.
Between 127,000 and my current 140k or so miles... I have replaced the following:
Economy tires with somewhat upgraded Toyo brand tires (helped a little with vibration as well as overall handling)
OEM Pontiac rims with an aftermarket set + new lugs and some new studs that needed replacing (Drag brand)
All 4 rotors and pads (also fixed 2 stuck calipers)
Both front wheel bearings
Multiple alignments
FOUR HUNDRED MILLION ROAD-FORCED BALANCES (hub-centric and all those little cute ways of doing it)
All 4 mounts/struts
Several inner/outer tie-rods (as of the other day they are all tight now)
Intermediate Steering Shaft
I have had this vehicle into SEVERAL shops and no one can figure it out, or I replace what they tell me and it doesn't affect driving at all.. I've spent hours online reading tons of different forums and have tried taking it places to try all the little tricks and still nothing. The hard shifting is a PCS issue so I'm not worried about it, it's more the vibration. The following have been checked and said to be in perfect working order according to several shops:
Both half-shafts (cv-axles) and joints
Several other different suspension components
tire pressure as well as balance and alignment
motor mounts (they are deteriorating a little, but have had them checked by multiple mechanics that say they are perfectly fine)
I am starting to lose sleep over this, like no really I should be in bed rn. So if anyone could please give any input I would greatly appreciate it. I understand a car with this many miles is going to have things wrong with it but I have driven 2 GP's with over 160,000 miles and they drove 10x smoother than mine and I have replaced over half of the car.
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