"Surging" in gear with brakes on at stoplight...

Car idles, runs and shifts great but in drive at spotlights and signs it "surges"..not bad, and with my foot off the brake it creeps ever so slightly, not like it wants to takeoff and it idles fine when I shift into neutral, but enough that you need to keep decent pressure on the brake to hold it back.
The transmission was recently rebuilt and it took quite a bit of tinkering to get the shiftdown linkage just right... maybe not?