Antique Rug Decisions
I imagine the opening sequence wasn't meant to make much sense immediately, but I felt that while I wasn't getting the whole picture, I was confident there WAS one. I like that in a story. It's important to signal to your readers that while they're confused now, you're going to take care of them, and they should trust you.
A small quibble- muscle memory is not actually stored in muscles in any way. "Muscle memory" is just slang for procedural or non-episodic memory, and just like any other kind, using it activates middle temporal cortex. Using muscles over and over has two effects: strengthening the muscle itself (increased volume of muscle spindles) and perhaps strengthening connections IN motor cortex. Nothing about nerve endings connecting more. All of the plasticity occurs in the brain.
But besides that opening bit, I found it pretty easy to suspend disbelief and go with your super cool premise. I like the moral quandries it brings up, and the way the picture slowly slides into focus as we figure out Tim's story and what happened. Though, not being a dualist, when terminology left "conciousness" and drifted into "souls", you sort of lost me. But I bet I'm an outlier on this, and most people probably didn't have a problem with it.
A major question I found myself pondering, though, was why everyone around Tim was so casually certain that he hadn't killed anyone, or if he had, that it didn't matter. I felt it kind of subtracted from the drama of the situation.
Much of the dialogue was fun and springy, and I really enjoyed that. Especially the scenes with Debbie. And when the wine bottle smashed voer the antique rug.
One thing that bothered me was the Mexican jokes, because I couldn't tell if they were being played for laughs by the author, or if it was supposed to illustrate something about how shallow Tim is. If the latter, then fine, if the former, not funny.
The pacing is fun and the whole thing very readable. Thanks for giving us something enjoyable!