Try cleaning around the hammer with a shot of brake cleaner and relube with just a very little bit of light weight oil. Sometimes the visous drag of too much and too thick an oil will act like a shock absorber to reduce the final velocity of the hammer. It's like the difference between waving your arm in air to waving it under water.
In the end though if you still have misfires try finding a little bit of metal or hard plastic tubing that will fit over the shaft of the spring guide before you slip the spring into place so that it puts just a little bit more preload into the spring. You won't need much. Maybe 1/8 to 3/16 inch at most. And it'll need to be a small diameter to avoid fouling against the frame or mag guide. Check for any sign of touching of the shim before you replace the grips.
A Shadow was my first firearm. And it's been a fantastic shooter for me. If for some reason I had to sell off all my guns except for one it would come down to the Shadow in one hand and my S&W Model 19 in the other and then my brain would go into meltdown trying to decide. It may be blasphamy but I'd have no trouble letting the 1911 in .45ACP go but the Shadow stays.
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