Finally ! Tried one last thing, the board did not expose the tx0 and rx0 pins so I took it upon myself to change that ! I unsoldered the resistor on the tx/rx pin, effectively cutting them from the USB to Serial (yeah called it usb to uart before but realised I was naming it wrong) then soldered 2 wire on the resistor pad on the 2560 side, then connected one of my own USB to Serial converter and voila ! Estlcam was able to upload and then connect to the chip and it work ! So the USB/Serial chip they are using on the board seem to be the problem, dunno what could cause this tough.
I’m leaving this message here for anyone searching the forum for the same info : Don’t bother. Its really not worth it to risk scrapping the board to accept Estlcam’s firmware when there are other mutch better way to go about it using other available firmware. If you really want to use Estlcam, drop the trigorilla and get an uno/grbl mega/ramps or other compatible hardware. I only really did it cause I’m a single minded obstinate fool as my wife would say !