At issue when coming to stop

So I just got a new engine and tranny put in my car, at first I
didnt really notice since I haven't driven it in a while but,
when I am almost at a complete stop my car lurches and I
can hear a noise from transmission almost like gears are
moving and clanking,  this is a new one for me, almost
sound like a syncro gear sticking or something,  any help
with this would be appreciated thanks