Where is my problem ?

I have a Transrotor Fat Bob TT with a Graham Phantom II arm and a ZYX Airy3 cartridge which is set up as well as I know how. My LAMM LL2 has dual volumne control so when I turn down one channel vs the other the left sounds slightly more congested or not quite as sharp and clear as the right especially on say, a trumpet hitting high notes.

Where is my problem likely to be? The Phantom lets you adjust lots of things like Azimuth, VTA, anti-skate. These are at the recommended settings. I've tried adjusting these but can't get the sound fixed.
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Is it in the recording? Have you tried different music?

A good way to identify the source of the problem is to try switching left versus right channel connections.

Once you identify the component that is the source of the problem, you could see if it is defective or only incorrectly adjusted.
Jameswei is right. Also, there may be no problem at all. If the image of whatever you are listening to is not exactly center, then the volume/loudness will be different for each channel. For example, if the trumpet you are listening too is to the right of center, then it should louder in the right channel.

Its also possible that the volume pots need to be cleaned.
Try switching the tubes from channel to channel on your pre-amp. It's possible one of the tubes is responsible for your problem. If after you switch the tubes your problem remains in the left channel at least you will know it is not the tubes in the pre. BTW, I thought the Lamm was a line stage, what are you using for a phono stage?
Sometimes newer vinyl of the same recording fixes the problem too. Maybe this vinyl had been played too much.
Do you have a fozgometer? with it, you can easily check to see your channel balance and crosstalk and adjust azimuth to reduce crosstalk between channels.
I would recommend that you borrow or purchase a good quality MONO recording and try changing your volume while it is playing, as you described above. Stereo can create the effect you describe just due to the nature of the recording. Also, I recommend you purchase the Cardas Frequency Sweep record. It has many tracks dedicated to trouble shooting and will degauss your cartridge and clean the stylus as well.