Deliberation and determinism

1. If (a) were I to do A, p would be the case but were I not to do A, p would not be the case, and (b) I can rationally deliberate over whether to do A, then I could rationally deliberate over whether to act so that p would hold.
2. For no proposition p about the past could I rationally deliberate over whether to act so that p would hold.
3. If determinism is true, then for any action A I can rationally deliberate over, there is some proposition p about the past such that were I to do A, p would be the case and were I not to do A, p would not be the case.
4. There is an action that I can rationally deliberate over which I will not actually do.
5. Therefore: Determinism is not true. (By 1-4)

Lewis denies 3. He thinks that if determinism holds and A is an action I won't do, then were I to do A, the past would have been the same (except maybe very close to the doing of A), but the laws of nature would have been different. This is implausible. The laws of nature govern events and one should not choose a counternomic interpretation of an ordinary counterfactual. But if Lewis is right, then we can modify the argument by replacing (2) with:

6. If determinism is true, I couldn't rationally deliberate over a proposition solely about laws of nature.

and replacing (3) with:

7. If determinism is true, then for any action A I can rationally deliberate over, there is some proposition p solely about the laws of nature such that were I to do A, p would be the case and were I not to do A, p would not be the case.

One problem with the above argument is that one can deliberate about the past or about the laws of nature when one does not know that one is so doing (for instance, one might speculate whether to make it be the case that E happens at t without knowing that t is in fact in the past). I suppose it is a stipulation about how I use "rational" that I won't count that as rational. Perhaps a different word than "rationally" should be used, like "properly": I cannot properly deliberate over the past.