1998 Kenworth w9. Wont start, Starter staying engaged after key removed

98 Kenworth w900
N14 cummins. 13 Spd

So, I haven't started my truck in a while. Probably close to 5-6 months. Been sitting in my driveway.
been doing some repairs on it, no electrical. Being that I haven't started the truck, I put brand new batteries in the truck.

I go to start it and it just sounds super weak cranking. But no start at all. Not even with starter fluid.
Start just looking around and then go to try and start it again. Cranked for about 4-5 seconds and I stopped, but it didn't stop cranking. Key removed and the starter is still cranking over. About 5 seconds later, it stops engaging the flywheel, but the starter continues to hum for about another 15 seconds and then stops. I was trying to run and get a wrench to disconnect the battery, but it stopped before I got it.

Is my starter bad or is something else going on?

 

Well, It wasnt doing a looong crank. It was cranking no problem but just, weak. I'm not sure how to describe how it sounded. But it wasn't doing a slow, long crank. I just installed brand new batteries in the truck yesterday.