I'm not and expert, nor do I have experience with the V6 5spd 3G/8G platform. However take this or what you can from this tidbit/info/2 cents, I had an 01 3G Gt with the sporty. Never lowered it, I owned it from 5yrs, I took it from 68k to 152k. Maintenance included Timing Belt and Water Pump halfway into ownership. Did plugs twice and axles once or twice not sure, endless brake swaps (pads and rotors) and thats it, never touched the suspension components period. I always had that annoying vibration climbing upto and past 30, new axles only reduced it a bit for like 5k miles. It never really went away andbi didn't really let it bother me. I now have this 01 GtZ with close to 200k on it, axle boots are torn and grease is everywhere, have the axles just haven't done the job since I want to replace the conrtol arms (which I haven't bought) at the same time. Moves strong no signs of giving up.
Point of my post is [Auto weaker than Manual] the V6 autos are supposed to be weak, and have a tendency to give out, sooner than the I4's. My 3G held for the 5yrs I owned it, with vibrations and the day I sold it, it pulled as hard as the day I got it. The GTZ now has 196k, got it with 193k, still going. If the fat pig auto can hold I don't see why the 5spd, that is stronger/sturdier won't.
I think it was just it's time to go, maybe a hard part broke internally and it probably would have happened with or without the vibrations. Drop it, open it, fix it with new fluids and be back on the road. Hope it helps or provides you with something to think about.
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