I listened to your Soundcloud sample. In my opinion, the reason your pops sound inconsistent with your slaps, is that your thumb-slaps are
legato (allowing the notes to ring out for their full duration) whereas your finger-pops are
staccato (short sustain, with more silence between the notes).
My suggestion is to practice controlling the
duration of your notes: Experiment with short, staccato thumb-slaps, and vice versa, experiment with long, sustained finger-pops.
I also agree with the comments above, that your tone is "brighter" than I prefer, though that of course is a matter of personal taste.
I disagree that you need to go shopping for a new bass, amp, effects, strings, etc. You are well withing "striking distance" of a good slap tone, with the gear you have now.