With the story I've been writing (found in my signature), I have been trying to create tension by slowly building the plot.
My concern is with whether or not I've been building it too slowly. In my latest chapter my character has had his first real power up, but it fell short of reader expectations. 

A little backstory: My character got summoned to another world and pretty much sacrificed his class and race bonuses as well as all of his stats. In return he gained the ability to evolve. I haven't explicitly said so in the story, but his memories as to why he wanted to evolve were also taken from him.

So, he gets his first evolution. It is a mini-evolution and he kind of rushes it because he had other things going on. In my mind he rushes it because he doesn't remember how important it is to him. Also, I want to keep him semi-weak for a big plot twist coming up.

Should I  
A) Explain this sentiment to the readers
B) Rewrite it to be more fulfilling
C) Introduce the plot twist early and change the format of the plot progression (It wouldn't really mess anything up)
D) Just keep on keeping on 
E) Something else

Don't worry guys. I figured it out

A quick note: the memory loss concerning why he wanted to evolve feels, to me, a hand-wave to avoid explaining to the reader why he made this huge decision. A reader might think that the character's loss of memory indicates that the writer is not sure why he did it either. ;)

How did you end up resolving it?

That is a good point about the memory loss and I may go back and tinker with it in the future.

So my character's mini-evolution gave him a Lesser Monster Core. My magic-ish system requires everything to gain energy from somewhere in order to use energy. The main energy provider is "Source" which at this point can basically be referred to as magic. Different applications are incoming, but not for a while.

So his Monster Core is supposed to alter him in some way, but it needs energy to do so. I made it so that there is this big initial pulling and purifying of the ambient Source. Like a start-up cost for the Core to run on it's own. Well, taking away the pressure of the Source, I gave him a moment of semi clarity to self reflect on his actions, their consequences, and his goals. The implication being that 'the powers that be' are using the Source to mess with his memories.

He wrote himself a To Do list to help him if his memories fade again, which they did. The list ends up being a bit cryptic and without the context of his memories, he interprets it in odd ways.

I should probably ask my readers how they felt about it, but sometimes I feel like I'm pestering them.

Has anyone complained about being pestered? It seems Royal Road offers a kind of interactivity and instant feedback that writers weren't able to get a generation ago. (Also, I think if readers aren't interested in polls or notes or questions, they'll just ignore them and read the story.)

What if the "energy" required is partly mental? Thus, as he fuels that Core, his memories fade or disappear entirely.

Nobody has complained about being pestered. Actually, as the story goes on everyone is getting a lot more vocal, which is nice.

The mental thing is a decent idea, but at this point I'm 8 chapter and 16k+ words dedicated into the other idea. I'll consider it for a rewrite though.

I think what you said above makes sense. However, I'd caution against adding increasing layers of complexity while trying to fix these sorta things. Not knowing that it removed his memories doesn't need to be a malicious act of some god or whatever, it can be a simple mistake.

To answer your original question, SeaGangster, I would go with:  D) Just keep on keeping on.

You will never meet everyone's expectations when it comes to a story, especially one that is still developing.  But the truth of the matter is, that the reader does not know what you know about the story and he/she can either be patient while you build that tension, or they can move on to read something else.  Only you possess the full scope of your story.  If you rush necessary development to please the readership, you risk losing something in the process.  Listen patiently to reader suggestions and advice if it helps strengthen your tale, but never sabotage your long-term story line just to please people.  Unless you're writing a choose-your-own-adventure story, then stick to your guns and stay faithful to what you know about your own tale and how it needs to develop.  Just my 2 cents ;)