yep, as far as i know, the anti slosh module is for the fuel gauge, and the gauge voltage regulator is for the other gauges (something about hysterisis, as Michael Y. puts it). keeps them from oscillating with voltage output changes (like how aftermarket volt meters twitch with each pulse of a turn signal).
i dont see how fuel could affect the performance of a float. floats still work, even if submerged in water....unless it rusted and stuck. of course, if the float has a leak, it will gladly fill up with any liquid.
about the only thought i have for testing if the A-S module or sender is at fault is: grab the sender wire between the A-S module and the sender. assuming it sends ground (it should), ground the wire. if the gauge position changes, to me, that suggests the A-S module is allowing the gauge to move properly, and suggests the float is bad.
with the above test, if the gauge did not move when the sender wire is grounded, i would guess the A-S module is bad (not allowing the changing signal to get to the gauge).
you could also check resistance in the wire before and after a fill up.
good luck.