How to Rebuild Trust?


I am a married < 3yrs, 41yo male recently-diagnosed with ADD:Primarily Inattentive. My non-ADHD wife and I are miserable. The dynamic I describe below is now one of our most common causes of conflict and a serious barrier to effective management of ADHD in our relationship.  I'm a long-time lurker here, and am looking for any insight the wonderful people of this forum, especially the non-ADHD spouses, may have to offer.

Although related to shame; this issue is more specific to the erosion of trust in my relationship and the struggle to rebuild it. A life of adaptation to ADD and an unforgiving and violent father who wants the right answer yesterday, means that I have developed an insidious habit of impulsive speech including the making of excuses when asked questions where I either:

1. Don't know the answer in 1 second.
2. Know the answer but believe it will get me into trouble or put me under suspicion.
3. Didn't hear the question well enough to answer it correctly.

The problem I'm having is that when I am honest, my wife is so jaded from past experiences that she doesn't trust me. To her, every reason that is inconvenient for her to believe is an excuse. In her mind, I'm always avoiding responsibility. There seems to be no convincing her otherwise. I can't even get her to understand the difference between a reason and an excuse.

Last Friday: The two front tires on her car need to be replaced, one of which was nearly bald. We are at a restaurant, discussing our plans for the coming days. We discussed a few options for getting the tires replaced. We settle on dropping her car off at the dealership before we head to out of town on Saturday and picking it up on our return trip, Sunday evening.  During this conversation, I didn't mention that I was off-work Wed and Thu of next week and could, if she liked, take the car in myself to have the tires replaced while she was at work. 

My wife is furious that I didn't bring this option up in conversation. She believes it's evidence of my:
1) Not knowing my schedule (irresponsible) and
2) Not stepping up to help her plan our week (uncaring)

What I told her: I wanted to get them replaced sooner rather than later because it had been raining a lot lately and I was concerned about her safety. In fact she complained about hydroplaning while driving last week. That's why I didn't even think to do it next week. I also just wanted to get it done.  This is the truth, as and ADDer I don't put anything off I don't have to, ever.  I'm terrified of forgetting things and like to get things off my to-do list ASAP.

She is convinced this is an excuse used by me to avoid responsibility for:
1) Not knowing my schedule (poor planning)
2) Not offering to do it next week when I was off work (selfish)
3) Not wanting to do it (laziness)
4) Not "stepping up" to help her plan our week (apathetic, un-manly)

Of course the act of making the excuse itself is my avoiding responsibility for:
5) Not telling the truth (liar)

Yet, my schedule has been in our calendar for two weeks. I do things for my wife daily, all manner of cleaning and chores; I have no issues with doing errands or other tasks to help out. I have to be honest that I certainly don't want to do it...but that's life, you help out and do things you don't want to. Lastly, I did help her plan the week, it's just not the plan she wanted. In a sense she's accusing me after the fact by asking why I didn't I tell her I had those days off and offer to do it because she didn't want to do it this weekend? I'm in trouble for not thinking to offer to do it the next week when she gave me no indication that this weekend wasn't what she wanted.  When I ask her how would I know that she didn't want to do it this weekend if she doesn't tell me or look at the schedule, she replies that it's common sens eand I have none.

And when I say I get in-trouble for these situations I mean, she stopped her morning routine to take a strip out of me for it in the house. Later argued again about it at the car, then put her car into reverse when driving away, stopped, got out and came back to call me stupid, an asshole, fuck you, etc. before getting back into her car and driving off.

How could I have done this better? How do I get her to know that I'm being honest with her?

Thanks to you all!