Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder
First you have to find the point(s) of slop. By your descriptions I'm not sure you've checked the ft hub's adjustment and maybe other spots. Is the stem an adjustable angle one? The fork quite likely has some upper/lower leg slop, most used forks do.
The ft hub is checked by, when secured in the drop outs, trying to pull/push the rim side to side. If the hub adjustment is loose you'll feel a bit of "rock". If the wheel were removed from the fork this rock will be felt by grabbing one end of the axle and doing the same push/pull towards the rim. At this time the axle's lock nuts/cones being secured against each other can also be checked with cone and locknut wrenches.
If the stem is an adjustable angle one there can be slop within it's hinge. Sometimes this play will not be eliminated by tightening the hinge bolt and the angle controlling bolt (and they can be the same bolt). But this slop is easy to see if looking fo it.
The suspension fork legs/bushings slop can be checked for by locking the ft brake on and rocking the bike for and aft. Much like checking a headset. But then rotate the fork 90* and repeat. Headset slop is evident in both checks. Fork leg slop will usually be far greater in the wheel being pointed ahead direction and far less when turned 90*.
Other areas of flex/slop can be the brake itself, the spokes being REAL loose or central/rear slop points that are mistaken for ft end issues. Andy.