Frequency response off with test record

ctlphd, it would help if you could report that directly in Hz and dB off.
No system is perfectly flat and cartridges will roll off at both ends. Depending on your scale this can look pretty scary but you may only be down 3 to 6 dB at both ends which would not be out of the realm of normal. 

Nothing to do with loading which affects treble region. Also given your vague description you might be looking at a benign bass rolloff. At what exact frequency? Is your scope calibrated? Are you accounting for the RIAA effect on frequencies below 500Hz?

Depending on your scale this can look pretty scary but you may only be down 3 to 6 dB at both ends which would not be out of the realm of normal.

I wasn’t thinking about it being a logarithmic scale, so it’s not as dramatic as I thought.. The change was close to double in amplitude, so approaching 6 dB. But, I thought typical frequency responses were flat within about 1 dB for cartridges.

At what exact frequency? Is your scope calibrated? Are you accounting for the RIAA effect on frequencies below 500Hz?

Unfortunately, I haven’t had time to go and measure the exact frequencies at which this occurred. That would require me to actually do some work :), as they don’t state the frequencies on the record. It is however midrange/upper base, and not low bass frequencies that are elevated. I’m going from memory of the waveforms on the scope that it was probably around 250-500 Hz where it was elevated. It does roll off after the low bass as well.

I am measuring after the phono stage, in the tape outputs, so shouldn’t the RIAA effects already have been compensated for?

"around" is not good enough. Get a test record that reports the frequency such as the Hi Fi News Analog Test Record so we have a better idea what is going on. Right now just listen to music and enjoy. In the end what are you going to do about this, get a new cartridge? I think not, especially if you like the sound of the one you have now.