the dealer will install 7mm bosch we reccomend 8mm magnecors, all of the O2's should be replaced at the same time. Do the plugs and wires first, did you do the rest of the 60k service sticky in the disco section? finish that before installing new O2's. Come back with the codes after all of that maintenance is done. what is the mileage on your truck? you should add that to your signature for future posts.