Have you checked all the underhood wires??? If these are cracked it will be the source of your loss of power and maybe even the pinging. Check the wires on the fuel rail....I'll bet you $5 they are cracked. Read
this. This. and this! If there is a rattle around 70 mph it may be the sway bar link, if it's bad...it will rattle. The test is to push in the clutch and see if the rattle goes away. If it does....replace it. The parts $9 each (one on each side)and it should take an hour or so to replace both (longer if you aren't too familiar with working on cars).
Good luck!
