Hello! I have an 05 Corolla S (AT) with about 330k miles on it, originally purchased at ~280k miles. From the looks of it, the transmission/tranny fluid was NEVER touched once in the life of this car. Fluid was black upon drainage 2 years back. Filled and drained it 3 times ((wasn't interested in cars like I am now and didn't really know what to do besides put new fluid in)).

Fluid still dark of course, just mixed with new fluid and some Lucas Transfix because I didn't know what I was doing, lol. Didn't see any metal shavings in the initial drain, although I didn't drop the pan.

When issues first began, a deep hum accompanied the code p0741. Gas mileage took a hit, sluggishness began. The car still shifts, it doesn't "lose power" going up hills or stall. Shifts are smooth, no reversing issues or any of that. Car DOES hesitate and stutter at times, at which I usually let go of the acceleration then press down again to get it to stop.

Regardless, two years later and the transmission functions the same. Just slow/sluggish to get up to speed, gas mileage and a deep hum aside from the stuttering (which could also be from codes p0455, p0441 and p0171, the only other codes that exist on this car).

Where do I begin with this? I keep reading it's the TCC solenoid, and a flush/fill and change of filter. Possibly ECM, as I've read from some people in Toyota forums that they've been recalled for years 04 and 05. Some replace the torque converter, others replace the entire transmission. I'm trying to look for something DIYable if possible.

Oh, and the original p0471 code disappeared. But I know there's still related issues. Not sure when it disappeared or if that's relevant.

Any advice or help would be appreciated. The last thing I want to do is get rid of my trusty Toyota.