Don't know how much help i can be but i'll give my imput. I've been shootng Thunderheads for 16yrs and i've never had a problem what so ever getting them to tune and group with any set-up i've used them with so i've never had any reason to change to something else. However, if i did ever change it would be to one of the two you've mentioned (Slick Trick/Muzzy). I don't know much about either of those other than i have friends who have been shooting Muzzy's for as long as i've been shooting Thunderheads with great success.The only negatives i've heard from Muzzy's/Tricksis in reference to blade sharpness not being up their with some of the other brandsbut this can quickly be changedwith a good sharpening stone if your into sharpening broadheads. I don't think you would be unhappy with either of your choices but personally if i didn't shoot Thunderhead'si'd probably be shooting Muzzy's.
You said your current set-up was new, could be you just need to let things sort of settle down and get use to everything then keep working with the Thunderheads. If their accuracy was good before there's no reason why you shouldn't be able to get them back to that point. If for some reason you can't get the accuracy you desire with them then i don't blame you at all for trying something else because confidence in your equipment is everything.
I love Thunderheads and after 16yrs with them i've got such a good inventory built up i'd be crazy to use something else.Good Luck and let us know what you come up with. God Bless! Mike