RICK - The 2-3 yrs I drove that White w/903 I mostly beat back & forth between Davenport IA & Chicago, about 3 hrs one way all the time but I did run longer runs, Detroit, Kansas City, St. Louis. Truck was a Day Cab with no sleeper bunk. Pretty basic truck, ordered out by Standard Forwarding, JD's captive contract carrier at the time. Company I drove for had 5 of them if I remember right. And THEY all smoked bad too. Especially in cold weather if You let them idle for any length of time, a gray nasty smelling smoke.
I averaged about 4 to 4-1/2 MPG in the summer and in winter with blended fuel I dropped to about 4. Not good by today's standards but I was loaded to around 75,000# gross most of the time. But I remember the day I first paid $0.60/gal. for fuel. Wish I could get fuel for that price now!
Company I drove for didn't have much of a maintenance program, they just patched things up when they broke to get You back on the road. Things like oil changes and grease jobs just didn't happen.
Truck was a '79 RoadBoss II, only had a 144" wheelbase and Reyco 4-leaf rear suspension so it rode pretty rough but the only other things I didn't care for about the truck was the lack of power steering, could have used a few more gears, only had a 6-speed Spicer trans, and it needed a 10-speed Road-Ranger with some overdrives, had 4.44 rear gears and was governed to 67 MPH @ 2500 rpm. And another 30-40 gal. of fuel capacity would have been nice, they only had one 125-130 gal. tank and in winter after My multi-stop runs I'd have to buy fuel to get home.
The cmpany had a mixed assortment of other trucks, couple S-series IH tractors, lots of Tran-Star IH tilt-cabs, an Astro-95 GMC, CL-9000 & L-9000 Fords, couple White RoadCommander's. Lots of 6V-92 turbo'd Detroits, and a couple 290 Cummins and lots of 350 Cummins. The one TranStar had an 8V-92 turbo'd Detroit, rated about 435 HP w/9-speed R-Ranger. Would run 75 loaded into a headwind if You kept Your foot in it hard enough, and got a whopping 3-1/2 MPG while doing it. But it carried 300 gal. of fuel.
From what I've gathered from other websites the 903 was used in some other military vehicles, like the Bradley armored troop carrier. Rated at about 600 HP which was quite a jump from the 320 HP @ 2600 rpm My truck was rated at. Guess they made a decent boat motor also. They didn't make quite as much torque as the 855 cid in-line 6's but they pulled pretty good from 1700 to the governed 2500 rpm limit, I just needed a couple more lower gears to keep it running in that range.
I'd driven a ready-mix truck back in the summer of '75, a '74 Diamond Reo w/555 Cummins & 5-spd Allison automatic. That 208 HP engine was no match for a truck that was loaded to over 50,000# all the time, especially with the Allison A/T. That was a tough job for a truck, idle around for an hour waiting to load, run the snot out of it for a half hour getting to the pour, idle for another hour unloading, then run hard again back to get another load. Everytime I drive My '96 F-250 Powerstroke I think about how it would run grossing 52,000#, My PSD actually has more HP than that 555 did!
3406 is a good motor. I read all the posts on the diesel pickup sites about "Real diesel engines are in-line 6's" and laugh. Most of those posts are made by people who've never driven anything bigger than a diesel pickup. Between My Dad & I We have logged over a Million miles on V-8 Cummins engines in class 7&8 trucks and there was only one night when My 903 swallowed some water and I bent two connecting rods and I couldn't drive it home. And Dad's '74 RoadBoss w/903 threw the fan thru the radiator one night but that wasn't the engine's fault. I'd take a V-8 903 Cummins over ANY comparable Detroit and a 555 over a 3208 CAT any day. They aren't as good as the engines avail. in trucks today but they were better than most available 30-40 yrs ago. Buddy of Mine drove an S-2200 IH W/ 6V-92 TTA & 9-speed, He'd run right with Me all the time, engine was rated 300-310 HP, and He got close to 5 MPG, but first thing every day He'd add a gallon of oil THEN pull the dipstick and see if it needed more! I'd add a quart or two of oil in My 903 once a week running 2500-3000 miles.