2004 Chevy Impala transmission slippage and speedometer not

I recently purchased this vehicle. On two or three occasions when starting off on a hill, the transmission seems to slip and then slams into "gear". Afterward, it appears to work normal.
Secondly on a couple occasions the speedometer stops working and will drop to zero. Last time it did this I could hear a ticking noise as long as the car was moving which would stop as the car stopped. It appeared to coincide with each revolution of the wheels. What do you think?