I have found that the best way to find the origin of any slop is to put your fingers on the parts you think might be loose so that it touches both parts while moving it. Your finger is VERY sensitive to the movement of relative parts that it is touching at the same time. This works for BB's as well as it does for headsets. Put your finger on the junction of the BB and the crank and wiggle the part(s). Put your finger on the pedal spindle and pedal junction and wiggle the part(s). Keep putting your finger on different areas and wiggling the relative parts until you can feel things move in directions/axis that they should not be moving or with more slop than it should have. Just keep trying until you find it.

Working on the pedals/crank/BB is much facilitated by a work stand where you can get the parts of the bike you are working on up to eye level and the rear wheel off the ground so you can move it freely in all directions/rotations. The source of the slop should become evident when you do these things. Bending over or crawling around on your knees with the bike on the ground makes it hard to see/feel what you are doing.