This time of year it's a piece of cake.
You might want to try to leave a little earlier, because it will be THE most scenic part of the whole drive. Glennwood canyon is spectacular. When they put the road through, they adapted the road to canyon, so the west bound lanes are elevated above the eastbound.
I have done that drive many times. 3.5 hours is a "no stop" pace without worrying about speeding tickets. That is from the west side of Denver, you would have to add the time from where-ever you start from. When leaving Grand Junction, take a detour through Colorado National Monument, well worth the drive, and is kind of heading the direction you are going. Start at the entrance in Grand Junction. If you start early enough to catch the rising sun, breath taking.