troubleshooting an issue with my gas fireplace

**Looking for some insight/suggestions to address a problem concerning my propane gas heat and glo fireplace that has a pilot light assembly with both the thermocouple and thermopile. On on the recommendation for my technician i replaced my whole pilot light assembly due to a pilot light flame and thermopile issue. My problem lies with the flame decreasing when I switch from the pilot mode to the on position. In pilot mode the pilot lights up with no problem and a very strong flame which engulfs both the thermocouple, as well as, the thermopile. As i m,ove it over to the on position the flame starts to decrease. I can move the knob slowly towards the on position enough for the main burner to engage, but if I move it over enough to fully open up the main valve, the flame no longer covers the thermocouple and/or thermopile enought to keep the millivolts needed to properly run the main valve. the reult is a clicking sound and suht off of the whole system. Also, I notice that the control valve for the main burner which regulates the flame itself has no impact on the intensity of the flame. Since it is a brand new pilot light assembly and the millivolts from thr termopile are strong, I believe the problem lie in the gas valve itself. Wall switch checks out fine and all the connections seem to be in order. Any insight would be welcomed. Thanks, Tom