In that kind of truck, on a route that you are not familiar with,
*take your time*. You'll get used to driving the truck, but remember that braking distance is still MUCH longer than a car, and acceleration as well.
Take I 80/90 out of Chicago, hit 65 S until just above Indy. Take 865/465 E to I-70E. A few hours later, you'll get near Columbus. I *STRONGLY* suggest you take the
I-270 SOUTH bypass. In case you don't remember the number I-270, follow the hazardous cargo signs through Ohio, and that'll take you around Columbus, instead of through it. I-270 south will become I-270 E. You will want to take the I-70 E exit, to continue east. If you happen to be hitting the Columbus area around rush hour, for your sake, stay in the lane as far to the right as you possibly can - many cars will be happy with you, and it's easier to take the correct exits that way during rush hour.
After you're back on I-70 E, on the other side of Columbus, I personally don't see why taking I-70 toward Baltimore is much of a problem - I-70 includes the Pennsylvania turnpike, though. I'm not really sure why you want to avoid it... ask whomever suggested that you avoided it for advice from that point.
Columbus will be just about as close to the middle of the trip as you are going to get. I make it from Chicago to Columbus in my car in about 6.5 hours - I would venture to guess that in a truck, it will be closer to 8 - 8.5 hours. Anywhere around Columbus would be a good place to stop for the night. Try to figure out exactly where you will be stopping *before* you depart.
I also suggest you find a CB and put it in the truck, and make sure it's working. They can come in very handy if you're in an unfamiliar area after dark, and need assistance or directions (*ahem* not that I would know or anything *ahem*).