Short of weather the worst grade is the final few miles up to the Eisenhour tunnel. Thin air of high altitude & steep grade will have you wondering when it will level out. Essentially from Denver to the tunnel is uphill. You can almost watch the fuel guage drop. One steep section of 70 just west of Denver can be avoided by going up Clear Creek Canyon out of Golden. Steady grade. Very spectacular canyon with a few tunnels.
Keep in mind that March & April are Colorados snowiest months. Pay attention to weather forcasts. I 70 is no place to be caught in a snowstorm or icy roads though CDOT does have equipment, & they use it.