Traction control, stabilatrek, low voltage, trouble starting, rpm gauge not working.

[S.kacz]

Recently changed my starter, and then ran into all these issues. Fuel mileage went from about 15 down to 11, trucks running rough.
Tested the replaced starter to find out that it was still good, so I reinstalled it.
Just bought an alternator still have to install it... Can someone share any thing over these issues.?