2002 Nissan Sentra "replace top end gaskets 02" Questions

...replace it or the wires, do so 1 wire at time not mixing them up. do not test for spark with other HV WIRES/spark plugs removed,do them 1 at a time, or it will LIE TO YOU, wasted spark is cool but ...

...replace the upper/lower gaskets. The engine runs ok at low rpm, but very weak at higher rpm (2500 and above). It is very difficult to get past 3000 rpm. Very low power. Would the intake gasket cause ...