I have a High Speed also. Here's my input.

Make sure all your screws are installed on the CPU board. If you are missing any screws, the grounding isn't as effective and the board will radiate a lot of EMF noise into the audio circuit (especially the Lamp Drivers as they are pushing a lot of current).

Hard to say, but... check U45 (7402). The kickers and Pop Bumpers are special solenoids that aren't controlled directly by the CPU. The switch inputs feed into the Logic gates of U45 and drive the solenoids directly (saves time for solenoids requiring fast response). U45 is associated with both kickers and the right and lower left Pop Bumpers.

G

If the wire for the coil is going to 1J8 then something is hooked up wrong.

From the High Speed Manual:
Right Jet Bumper - Special #3 BLU-ORN 1P19-3 Q73
Lower Left Jet Bumper - Special #4 BLU-YEL 1P19-6 Q69
Upper Left Jet Bumper - Special #5 BLU-GRN 1P19-8 Q77

If you need a copy of the schematics, you can download the service manual from
http://www.ipdb.org/machine.cgi?gid=1176

G