2006 tundra no start no crank only clicks

My tundra 2006 doesnt start or crank it only clicks. But when i bypass the starter relay it does crank however it doesnt start still. I already charged the battery and jumped it with another truck. When jumped the battery needle goes to the middle however as soon as i disconnect it it drops completely. I changed my ecu because i was told it wasnt being read with one i bought online thats supposed to be plug and play. Fuel pump was recently changed. Also i realized the bushing on my shifter cable came off for some reason but i dont think that relates correct ?what could it be its been 3 mechanics that have seen it and none have been able to fix it.