If it runs right with the gen light on then I would suspect a spark issue. It sounds like your voltage regulator is a bit sticky, causing the GEN light issue, but also maybe making the coil resistor bypass relay stay on too. That would mean the coil is getting full 12 volts, making a hotter fatter spark, and make the truck run better or at least different.
Make sure the points are good and gapped right, and check the spark plugs for condition and correct gap.
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95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)
MEPR: Man, my 4x4 makes all other LUVs look good
