Pretty tall order---I'll leave it up to you how you avoid Grants Pass from Eugene---the easiest route out of Oregon to California to connect with I-5 is from Bend---but Eugene to Bend is nothing but mountains.
State 138 in California is not very hilly---long straight road (it's been a while) but you connect it at Gorman which means you have already climbed the biggest hill over Tejon Pass (the grapevine) but you avoid the backside which is fast and steep and long.
If you take 101 then you have the Cuesta grade out of Paso Robles to do; it is down hill 7% and about three miles long is all--- then go across the top of LA-- 101 to 134 then to the 210----it moves faster than going down further into LA---it connects to the 10 which takes you to Palm Springs. Still you spend a lot of time in LA--but this is the route I take a lot and have not been stopped cold by traffic ever but I dislike it as do you.
So it's hills or LA traffic pretty much---if someone knows a secret I'm tuned in to hear it.
It is called the LA basin for a reason it is rimmed by mountains--hard to sneak in there on flat roads.
I do all my own stunts
03 Dolphin LX 6355, Workhorse W22, 8.1 vortec, 04 CR-V, Blue Ox, Brake Pro----Norm, Barb and
Doc(He's a PhD)