Have a problem cranking over a 1995 SLS. It will crank eventually but takes a lot from the starter. Once had to let set for about 30 min before able to crank over.
What to check first.

 

It sounds as if your starter is going bad but before assuming this i would check wires on the starter to make sure everything is tight and has good connections. Next i would make sure your battery has a full charge or is not old and worn out. your battery (if its old) will cause your car to start slowly due to not having enough cranking amps. Some things you could do is check the battery itself by testing the volts should be around 11.8v to 12.5v without the car being on. If it shows up to be less than that (10.8v or lower) charge the battery if it is a fairly new battery, or change it if it is around 4yrs or older. Especially when winter hits and its cold, an old battery wont have the cold cranking amps to start the car efficiently. If the battery is good and connections are good then i would definitly suspect you have a bad starter.