freightliners almost always have a ground that goes to frame close to batteries other brands run ground wires from batteries to starter and have a thick ground strap off starter to frame and not so much of a parasitic draw but can cause random problems with out it truck will get more alternator wine in the radios and hard starting problems with a pretty bad voltage drop from batteries to starter and cab
Voltage regulator problem? None of the grounds are trying to be made to aluminum? Negative cables look good but melted/corroded under insulation half way back? Batteries big enough? Just throwing these out there.
I'm always having battery problems with the trucks I got. The Mack battery cables will loosen up from road shock every so often and not start.
The Peterbilt will draw the battery dead if it sits for a few days from the automatic transmission.
I have found new and rebuilt starters to only last a few months more than once.
Don't feel bad about it. I get tired of replacing the same parts over and over again too.
Need to check it when it's acting up.
If you have good voltage at the battery while cranking.
If you have done a proper (stud to stud) voltage drop on the positive and ground side. There should be no more than .5 volts on the positive side and 0.00 on the ground side.
Then it's the starter. Does not matter if it's 2 hours or 20 years old.
Good batteries with no loss of voltage to and from the starter what else is there?