It is all interstate so you won't have a problem. I-15 to St George and then SLC. From there I-84 to Portland.
You will have a few 5-6% grades along the way. One down grade is 5-7 miles going down into Pendleton, OR. Be sure to slow down to about 40mph at the top and gear down to 3rd gear or even 2nd gear at 35mph. Don't ride your brakes. When you need to apply your brakes, press hard to bring your speed down 15mph quickly and then stay off the brakes for at least 60seconds, 90 seconds or more is better.