My 2000 GMC Jimmy recently developed a series of

My 2000 GMC Jimmy recently developed a series of problems. First, the key could not be removed after shutting off the engine. I found the key release under the ignition switch to resolve that issue. Then the alternator failed. After replacing the alternator all was fine for a day then starting became a problem. When starting, battery voltage is good, but it acts like a bad terminal or starter connection. Connections were found to be okay. There is a lot of electrical noise and the starter turns slowly. Also, various lights come on in the dash, the tailgate window releases and the tow/haul light comes on. Sometimes the "security light stays on while driving and the driving lights sometimes do not come on. Any solutions?