My experience is that a bad alternator is often followed quickly by a bad battery (or two). If that is your case, you can throw in an expensive FICM later unless you check it out thoroughly now. A voltage test is useless. Do the load test on each individual battery. I do it at least twice a year now as preventative maintenance - and I have new batteries. I also recommend considering the installation of a fuel pressure gauge - it is a great tool to use in troubleshooting, but more importantly - making sure you don't let the fuel pressure get below 45 psig will possibly save you a big injector bill.