If you have messed with the wiring in that area you may have disturbed the coil connections, or the fact of just standing means possible corrosion on them which may not be allowing full current at higher revs. Worth a check.
My next port of call would be the earth leads to the frame.
Followed by plug leads and possibly new plugs.
If it persists I would find a bit of road where you can replicate the issue for 30 seconds or so, hold it at those revs and cut the engine dead and check the plugs to find out which cylinder is misbehaving
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