Either rotor phasing or fuel delivery. Caps and rotors are carbon copies and will not change rotor phasing. Having no vac adv makes it easier to sort out. Generally running the car up thru the gears if it is ign it will miss in all 3 gears at the same LOAD and RPM. If it's good at 4500 in 1st and 2nd then acts up in 3rd that points to fuel delivery as it takes time for the need to outstrip the delivery unless the fuel delivery system is EXTREMELY inadequate which I do not think is the case here. Whereas an ign miss will happen at the same load/rpm no matter what gear you are in. I'm thinking fuel but if need be drill the hole in the cap & check rotor phasing at idle. Ign sub issues; MAY need a rotor with a .060" longer blade NAPA Echlin MO3000 which helps some with phasing issues(& we can fix phasing directly) and check ECU ground and pickup gap but first let's pin it down to ign or fuel