There are a few spots on 40 & maybe 1 on 44 where there is construction & you have only 1 lane, but there isnt anything that will slow you down too much.

I just drove from Phoenix to Chicago this weekend & it took me 25 hours & 16 minutes of driving time to go 1782 miles (I took I17, I40, I44, I55), so I was able to average 70.5 mph or so including stopping for gas & food.

Everything slows down the further east you get though - from Phoenix to Amarillo I averaged 73.2 mph, but from Amarillo to Chicago I only averaged 68.2 mph, I bet east of there it will drop at least another 3-4 mph as you get into areas that have higher population densities.

The only suprise I had was I forgot about the time zone changes - when I pulled into amarillo it was two hours later than I thought it was going to be.

I think you could do the drive in 40 hours of total driving time - be prepared for some cramps for a few days afterwards if you do it in 3 days though...my legs and arms took a day or 2 to feel normal & you're driving about 1000 miles more than I did :)