As others have said, there's no problems at all coming out here to the Denver area. You'll have more hills/twisties in western PA than you'll have anywhere else along either I-70 or I-80. Keep in mind that it's a very VERY gradual climb from the Mississippi River to Denver via either route. There's some gentle rolling hills in Iowa if you take I-80, but certainly nothing more than what you're accustomed to in PA.
If you take I-80, when you get to western Nebraska, take I-76 from Julesburg CO toward Denver and get off on exit 31/Hudson exit for CO 52. Take that west all the way to US 287, that will put you on the south end of Longmont, and head north to whatever your destination is.