Unlike Fred, I DO believe the rising tone at statement ends came via Australian soaps. The few hours of weekly exposure to the speech patterns of the actual programmes failed to guarantee kids would NOT go on speaking thus to fellow-addicts in real life.
As regards aks, until around 1600, the regular literary form of the verb meaning ‘ask' was 'ax', based on earlier forms 'acsian' or 'axian'. 'Ax' remained until then the commonest form throughout the Midlands and Southern England, whilst 'ask' was essentially just the Northern form of the word.
It is, therefore, not just confined to specific racial groups but - even now - largely dialectal. I believe 'aks' is still quite commonly used in Lancashire, for example.