I had been playing guitar for a couple of years when i decided it would be cool to buy a bass so i could jam with my drummer friend, and play in a few more bands then i did...

two years later and i'm alot better at both bass and guitar but only really received proper instruction on guitar

so now i've kinda ended up with this weird mismatch of bass techniques. i can slap fairly well (play primus and RHCP no problem) but for the rest of my playing i'm still just using guitar techniques on bass....

so my question is

what should i be learning on the bass that i'm not going to be able to do purely with my knowledge of guitar techniques?
Well, it kind of works hand in hand with the kind of music you play.
Go and groove with a drummer for a month. I think one of the errors many people make when switching from guitar to bass is not learning how to provide a complete rhythm section with only drums and bass. Not only will it force you to think in new ways (you'll get very bored unless you work out more interesting, complex parts to fill the sound out), but it'll teach you the most important skill of all for a bassist which is locking in with the drummer.

Work as though you're writing a song for a whole band - don't just sit around and jam for hours, although that's quite good fun. Think in terms of chord progressions, where you'd put fills, and so on. Then maybe record it and put a guitar part over the top - which might well help your guitar playing as well, but will help show you how bass should work in the context of a song. Remember to keep the focus on what you're doing on the bass, though.

If you don't know a drummer, download Hydrogen - it's a damn good free drum machine - make up some simple beats, and go for it.
See if you can get a pro or better yet, a good bass teacher to give a few lessons. There's nothing like a bit of constructive criticism and pointers to push your playing in the right direction and fill in those gaps of knowledge.