If using Heis for the 808 you can turn up the glide so the note slides into the next one, instead of having to use release which can cause overlapping issues.
assuming you mean 808s from a synth, turn down the "release" module to decrease overlapping, and like Jordi said, make sure the notes themselves aren't overlapping.
If using Heis for the 808 you can turn up the glide so the note slides into the next one, instead of having to use release which can cause overlapping issues.