I think it's just a matter of practice; right now you're used to going through certain steps before making an action, and by adding more tables you're forced to use different steps and you're not used to it yet.
I think stepping down a level is fine. I'd really stress that multitabling will skyrocket your winrate, so practice it as much as possible.
I think I saw you were up to 25nl, so try going back to 10nl and just nutmine. Play nothing but premiums jamming them pf, and small implied odds
hands (33, 67s etc) in those limping spots in LP. It'll be extremely easy to play, and you'll get used to playing 4+ or 6+ tables.