95 k2500 7.4L electrical issues

i recently purchased a 1995 gmc K2500 pickup with a 454 TBI and 5-speed manual (nv?). shortly after buying it i started having issue after issue, i wound up replacing the "rebuilt" engine and since is running ok, it still has an idle surge every once in a while, still working on that, my biggest concern right now is when the truck sits for a couple of weeks it kills the battery, it seems to run low voltage but ive replaced battery and alternater checked all conections everything seems fine. when driving it at night with lights on everything goes dim and blinkers make the "check gauges" light pulse on because the volts drop so bad. i would think if there was a short it would have fried something by now but im running out of ideas, sorry for the story, truck has been a "work in progress" ever since i bought it. any ideas would be greatly appreciated
:banghead: