Dead battery- now a miss?

[mopar250]

Hey everyone- I have an 80 C10 that I did a 5.3 swap in a few years ago that has now has a miss. Last summer we drove it to a cruise night and when I got home, I pulled in to the garage and left the lights on when I shut it off and drained the battery. The next day, I charged the battery and fired it up, and it has had a miss ever since. The truck will drive, but misses pretty badly and I haven't had the time until now to mess with it. It has a 5.3, ls1 intake, headers, aftermarket harness and a GM computer with a "mail order" tune, so nothing wild. I have a set of the Dakota Digital gauges, and it isn't throwing any check engine lights. The swap has been done for about 4 years and I put probably 4000 miles on it since I finished it and never had any other issues so I'm honestly not even sure where to look first? Anyone have any idea's?