Output level inexplicably reduced- help

I have an Volume output level problem with my system. My electronics are Audio Research:
Reference 150 amp
Reference 3 preamp
Reference 2 phono preamp

Lyra Atlas cartridge

This system was running great for three years. Nothing has changed. Now, my highest output level is inexplicably reduced. I cannot get a volume level greater that about 90db. I just re-tubed my amplifier and expected that to solve my output level problem, but it didn't happen.

I have always run the pre-phono on low gain, load 50k. The sound was warm, detailed, great soundstage - everything was great.

Now, the only way I can higher output volume is to switch to high gain on the pre phono, keeping the load at 50, or 100k, it doesn't seem to matter much. I can get the big volume, but, the sound loses its smoothness and warmth. It has an edge if I switch to high gain.

Can anyone provide me advice? I would surely appreciate it.

Thanks

PS I'm not losing my hearing.