I think that this isn't a problem about rational choice given a certain utility function, but about what your utility function should be in the first place, and there's no "correct" answer to that question.
No one can tell you whether you should prefer to be tortured horribly, then given amnesia, then given $1 trillion, or whether you should prefer to be slapped and then given $100.01. Decide which one you would prefer, and how much, and then we can talk about constructing a utility function that accurately reflects your preferences.
Once you've figured out your preferences and assigned consistent utilities, then we can do the sort of mathematical reasoning you are trying to do. For example, maybe you decide that hell+amnesia+riches has a utility of -100 and that slaps+money has a utility of +1, for example by deciding that you'd accept at most a 1% chance of hell+amnesia+riches in exchange for slaps+money. Then we can immediately use this to, say, calculate what other bets you should and shouldn't take with regard to these options.
But we can't tell you which one you should prefer: you have to decide that yourself. You're allowed to prefer hell+amnesia+riches if you want!
So I have a conundrum. Imagine that Omega comes to you and offers you two choices:
First choice: You get a moment of moderate pain, let's say a slap and then another slap, so that your face hurts for a couple of minutes with some anguish. Now after that pain has faded and you still have the memory of it, Omega measures your discomfort and gives you exactly the amount of money that gives enough joy to compensate the pain and then a cent. By construction, the utility of this choice is one cent.
Second choice: Omega inflicts on you hell for a finite amount of time. Your worst fears all come true, you are unable to distinguish between reality and this hell, the most painful sensations you will experience. After this finite amount of time is over, Omega deletes all memory of it and gives you essentially unlimited monetary funds but still, this experience does not quite compensate for the previously experienced hell if you would remember it. By construction, the expected value of this choice is negative.[1]
If we go by expected value, the first choice is obviously better. Of course Omega forces you to take one choice or you will just get hell forever, we want our thought experiment to work. But if we go by the decision procedure to choose the option in which our future self will feel best, the second choice seems better. I have not yet found a satisfying solution to this apparent paradox. Essentially, how does a rational actor deal with discomfort to get to a pleasurable experience?
[1] I realize that this might be a weak point of my argument. Do we just simply add up positive and negative utilons to get our expected value? Or do we already take into consideration the process of forgetting the pain? Maybe therein lies a solution to this paradox.