You'll find that you're now picking up "as far south" as Galt PD, because, just like Elk Grove, Galt is on the Sacramento TRS. Sacramento has two trunked radio systems, and each has several repeater sites. In other words, there are two sets of frequencies, but each set is broadcast from several different locations.
Whether or not you can pick up Roseville depends on a lot of things. First, do you have Roseville programmed correctly? It is not just a matter of putting the correct frequencies in, you must also have the correct band plan selected. Roseville is a rebanded system, Sacramento is not (yet).
The second issue is probably your exact location. Sacramento is a huge place. Are you in the city of Sacramento, north of the river or south of the river? Are you at a higher place in the county or down "at river level"? I am in Fair Oaks, a relatively high location, and can pick up a huge area.
Lastly, what antenna are you using? The stock rubber antenna? If you are either some distance from Roseville, or at a lower elevation, an outdoor antenna (or at least one designed for 800 MHz and pointed the correct direction) will make a HUGE difference (assuming you use low loss coax, etc).
Bottom line here, it is not the scanner's fault. I can pick up Roseville from pretty much any place in the county (haven't tried from the Isleton area), so you should be able to as well. Welcome to RadioReference.com!!!