Charging system woes

[Big Port Jimmy 6]

87 r2500 01 5.3 4l60E with 25k miles on the swap. I have never been satisfied with the charging on this truck. Best I have ever seen is 13.8 at 2k rpm usually 13.2-13.4 at idle. Will not bring the battery back up if its weak and with the Headlights and AC the voltmeter plummets. I have wired it back to the stock wire from the lamp in the truck, I wired it originally to the PCM with no difference in results. This is the 3rd Alt. went from the low amp to the high amp unit first and the high amp unit had a bearing failure, but all charged approx. the same. Using a DVOM on the batt to get my readings. Is there a 1 wire regulator for these? Is there an old style alt that will fit the bracket? Thanks Jay