+1 for gib adjustment – a classic symptom of a 'sticky' cross-slide gib would be "put on a small cut, nothing happens; put on a second small cut, again nothing happens; put on a third small cut, and a huge cut comes off as soon as the tool hits the work" – the total depth is usually more than the sum of what you have dialled in because it often seems to include all & any free play that exists in the assembly, in addition.
If the gib is too tight for the first small movement to have meaningfully advanced the slide, a subsequent movement of similar small magnititude will often fail to find enough 'purchase' in the nut for the screw to hold itself – if the handle is 'going uphill', it can fall back under it's own weight as the screw 'backs-out' a part-turn, giving the impression of excessive backlash.
If you can back off the gib adjustment a bit, it will tell you immediately whether the fault lies there, or elsewhere.