Transmission thoughts

[Henn28]

Looking for advice on what I think is a slow loos of bottom end power on my e53. I had vaguely suspected that the car was getting a little slower at low RPM (below perhaps 3000 to 3500, but like a frog in hot water didn’t have anything to compare it to until the G05 showed up.

Without the electric motor that car makes 375 hp and has monstrous low end grunt. The 4.6 in my car makes close to 350 and is no where close these days. I realize that the 8hp and final drive could be all, or most of the difference, and that (I think) the 4.6 power comes in later due to it being mostly cams, but I also have had for a long time a very distinct whine coming from the tranny at all RPM.

The gearbox is a remanufactured one I had installed in late 2019 and although this was during the period of benign neglect the car went thru and my records suck from then, it’s probably got 25k or so on it. I’ve changed the fluid once (last year) and all looked good with just a little “mud” on the magnets.

The TC was advertised as new, but it didn’t look new when it went in, so it was likely remanufactured as well. Could a failing TC cause a loss of low end grunt/power without the normal low end shudder that comes with that problem?

I’m thinking of having a full flush and fluid change done since the regular filter change procedures don’t get anywhere near a full fluid change done. Beyond this, I do t know enough about trannys to know why it would be whining like a turbine and if it could be causing a loos of low end power without other problems (slipping, shudders, hard shifts, etc.).