The pitch error is probably caused by the use of integer math in oscil, oscili and oscil3.
I have developed the opcode 'posc' (precise oscillator) which is substantially an oscili
with floating-point indexing math. The sources of this opcode (as well as of all
DirectCsound) are available in my site:

http://www.agora.stm.it/G.Maldonado/download.htm

Greg Sullivan wrote:
> 
> John,
> I'm not sure. But, the problem I reported regarding the interpolation
> being very slightly off pitch affects oscili, in addition to oscil3.
> (recall that I originally posted my test orc & sco files which
> used oscili instead of oscil3, and the problem definitely
> existed even then, when I was using oscili)
> 
> Greg.

-- 
Gabriel Maldonado