The TX has a 3.8mm transfer port. The LGU is made with a 2.9mm port which tuners open to 3.3 to 3.5mm.
Possibly the TX port is to large when short stroked. The SCR is wrong and it creates a harsh firing cycle.
I may of course be wrong
I sleeved my TX port to 3.2mm and quite like it. It may be better at 3.5 but I don't want to ruin it.