Try to play the chords in the left hand in the middle C range, or even just the bass note in that higher register. Sometimes you might just want to omit a LH part completely. I play bass also, so I can understand the situation - I also have a tendency to use block octaves in my LH playing the keys.
Unless ALL you can do with your LH is block octaves you should be able to make a change, but it's not easy to alter one's style. But you can also try to keep in mind that playing solo is far different from being in an ensemble situation. When playing with others you generally have to 1) play a little less loud, 2) accept that there will be times where your part is counting measures of rest and 3) be aware that others around you have their own parts/ranges that their instruments cover better than you might.
Indeed, this tends to be a problem with many "garage" rock bands. No one in those situations usually has any legit enemble experience, so you get 2 guitarists playing almost the same part at ear splitting levels, and often overlapping in the range of the bassist...and then they wonder about the muddy mix they get. Add in a drummer who has no sense of how to play soft (or as many rockers do, equates "soft = slow") and you get a recipe for crap....