take the new one back to checker and get it tested. they do come bad out of the box every once in a while. if its an autolite rebuild it should have a lifetime warranty. i've got the starter, alternator, and track bar from them and had no problems with warranty on the starter or trackbar.the alternators still going strong. If your batteries are junk they might not take a charge anymore and it might look like the alternator is bad when it isnt. they should be able to test it on the truck. good luck!!!!!!!!
