Recently, we have reported on the use of the titanium-zirconium-molybdenum alloy (TZM) as an autoclave material for acidic ammonothermal growth of bulk GaN using chloride based mineralizers. Here, we discuss the trends of growths with temperatures ranging from 650 to 900 degrees C at pressures around 100 MPa in a TZM autoclave. The resulting crystal quality as measured by x-ray diffraction appears to be dependent upon growth thickness. Secondary ion mass spectrometry studies of impurities such as O, H, Cl, and Fe show a tendency to decrease with increasing growth thickness, with concentrations ranging from 10(18) to 10 (20) cm(-3 )for 0 and H, and 5 x 10(16) to 5 x 10(18) cm(-3 )for Fe. Cl did not have a standard to quantify the concentration. Ti increased in concentration with increasing growth rate with a range of 4 x 10(14) -1 x 10(17) cm(-3) . C had steady concentrations between 3 x 10(16 )and 5 x 10(17) cm(-3) and the Mo concentration was measured in the low 10(16) cm(-3) or less. Zr did not have a standard and thus could not be quantified but was near the detection limit in all cases. The instability of the ammonia solvent at high temperatures requires very high pressures for ammonothermal growth above 800 degrees C but short-term growth has been demonstrated up to 900 degrees C.