There is a glitch in the game, that allows you to continually decrease the amount of energy it takes to swing/fire/equip any item you synth. But, it was patched. In order to remove the patch, Just go to your dash, go to System Settings, Memory, then press Y while your hard drive is selected. Then "Perform maintenance" or something like that. Select OK. Dont worry about memory loss, it only deletes patches, not saves or DLC. Then just go into the game (DONT PATCH) and make the items that you want to be uber.
To make an uber item, Synth a low quality weapon (level 1 weapons work best) to a high damage high quality weapon (as high damage wep as youve ever gotten) and keep synthing low quality weapons to it. Eventually the energy required to swing will be so low you could swing endlessly without getting tired. Same thing goes for guns and stuff. When your done creating weapons, just save, go back to dash, then go back into the game and it will ask you to patch, select yes, and you can continue playing with your uber weapon!