What are high low henglong gear boxes. I thought they only had pot metal gears or plastic. At least as far as the Sherman is concerned.

that bad noise from your mato box is likely the same as I have described. Any gear that has its hole moe than a couple thousandths bigger than the shaft will allow the gear to wobble. I have worked on many many gear boxes commercially and in models smaller than ho trains. Clearance is what its all about, and these mato boxes are just junk.
The plastic HL box is actually bettter engineered for the job it is asked to do.