I recent purchased an Ibanez Sr500PB and it is goregeous. The bass plays very well except fornone thing.

I got a set of kaliums (.130-.55) to set this bass up in Drop C. CGCF. I got the bass setup at a shop who always do great work.

The bass will not stop buzzing on the C and F strings, near the first few frets. No matter how high the action, truss adjustment etc...

I feel as tho the strings are sitting too low in the nut in those slots. After all, the giant 130 doesnt buzz at all. I even upgraded from a 120 set to these and the problem is persistent.

So my question would be; would replacing the nut with an oem nut solve my problem?
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You need to rule out high frets first and check the neck for twisting, just in case. It does sound like a poorly cut nut though, which leaves you with two options:
1. Replace the nut and cut the slots properly,
2. Perform a light fret levelling job on the treble side.

The ideal action would be to strip the strings off, set the neck perfectly straight with the truss rod, check ALL frets and level as required (with dress and polish), fit a new nut BLANK, mark up the string heights with feeler gauges, and then cut to depth. Obviously you'd then restring, set action, and adjust neck relief again.

Or just don't bother if buzz isn't coming through your amp.