steering issues

Worn steering rack?

Did they do the tracking properly?

Far too many places will just slacken off one track rod end and wind it in or out until the average reading for both sides is within spec. This is the quick and lazy way to do it, and since most fast fit places have quite a low fixed price for tracking, is the way many will do it. They should centralise the rack then adjust both track rod ends, which obviously takes longer.
If they have done it the quick way, your rack may well be offset to one side, which if its only a few mm has no real impact, but a larger amount starts to have all sorts of unwanted effects on steering angles.

Aside from that, it could be pretty much anything. Start with tyre pressures, tyre condition and wear, then all ball joints and bushes, bearings, a brake binding slightly.....its a long list.