Thanks redhat, I take it you had to go by experience and not published info. When I drove the new machine to the shop after it was unloaded, 17.5 mph was about all I could get. I had it in 4th, but couldn't remember whether they had left the 4WD on while unloading. Since I'm new to red combines, I was more interested in dodging the traffic and watching for low limbs than I was trying to stop in the road to figure out why I was going so slow in 4th. With all the rain and mud I haven't gotten it back out of the shed to try out my 4WD vs. 2WD theory. I did not get the HI-LO option because I didn't think I needed it, but wasn't going to be too happy with 17-18 mph for top road speed.
Thanks for the reply,