(T) Steering Problem, any suggestions?

I have an 1994 M reg Punto SX which was always a heavy steering car. The steering has got really light and vague, almost slippy and not as responsive as it used to be. It actually veered across the road last week when turning left then right on a winding road. My garage changed two tyres and replaced the back shockers but the steering is still feeling wrong. The garage have said if the steering rack was the problem the steering would get heavier, and I wondered if anyone else had experienced this and got a correct diagnosis. Its worrying me when I drive it. I hope this makes sense as I'm terrible at explaining car problems.

Hope someone can help.

Thanks :D

1st thing has the tracking been checked?

The Fiat Cinquecento
Fun While It Runs

Is that the same as wheel alignment? If so, yes.

are the tyres over-inflated?

I dont think so, two have been on the car for ages and new are brand new from after the problem started.