Starting problems on 1987 COE Freightliner

Hello,
I'm having trouble starting my semi. 1987 COE Freightliner, NTC-315F also known as NT/NH 855. Since I bought it it had been starting fine until it got cold, I can't be sure if the cold has anything to do with it though. I tried starting it in the cold and it wouldn't start, sounded like the starter was jammed so I took a hammer to it and left it. the next day it started right up, it was a bit warmer than the day before.
About a week after: Now, I can't get it to start again, it has been getting colder. While trying to start it sounds like the starter is jammed and just stops working. A few times the starter stays engaged but sounds like its having trouble turning, slowly spins the flywheel in sputters and then dies after the solenoid clicks.
I have already cleaned all the connections, re-moved the starter and tested it and also the solenoid and they are working. Also if I move the flywheel a little bit, it feels like its getting stuck, and hit the ignition switch again it turns the starter but then dies.
Anybody have any ideas??

 

Oh, and I have newly tested and charged batteries in it.

 

Fuel looks okay, it's not black, no gelling either.

 

You are meaning, the cable or on the battery?? Is there another way to check them instead of heat?

 

The starter is back on the semi. I tested the voltage going through with a multimeter, tested the studs only and the same amount of voltage is going through them. I'm assuming this means they are okay.
I also UN-installed, cleaned, & tested the starter solenoid relay. It checked out fine, it clicks and has the same amount of voltage going through it with the relay on or powered.
The next thing I'm giong to do is check the voltage going through starter, I need someone to hit the ignition switch though so it will have to wait. I was told if the voltage is below 9 volts I will have a batt, cable, switch problem. If it is above 9v I will have a starter brush problem.

 

I will probably re-post what I find out on Monday. Thanks for your help.