couple of suggestions (these are basically assembled from my own reading of this forum)
- you say you're still struggling to keep in time. this is a big deal. practice with a metronome (
here's a free one). go slowly at first. also, practice playing along with songs on the radio/CD (this will probably also help your ear)
- you say you know chord progressions well. do you know the chord notes for a major chord vs minor? how about a dominant 7? these chord tones (sometimes called "triads") will be what you use when you're tired of sticking with the root. you can find all these online.
- other than that....practice. a little every day. practice your weaknesses, not just your strengths. keep playing with your band. maybe there's even one band member that'll do an extra practice with just the 2 of you.
good luck!