Living in San Diego it's just basically a fact of life that you have to deal with LA to go north. And I've gone thorugh way more times than I care to remember. As far as Fresno, I drive that route every march to round trip to Yosemite and have so for easily 20 years. Since you are towing a trailer I would just make it simple.
99S to 5s then take either 5 or the 405 whichever your navigation says is clearer. No matter what time of day both routes will have some slowing, it's more about when you go than which route you take.
I prefer the 405 but only because the ramp to stay on the 5 is kind of convoluted and narrow and easy to miss.
As far as time, figure you are about 5 hours from Pendleton so sit and figure out the times. If you hit it right it will take 3 hours from the bottom of the Grapevine until the south end of Orange County when the traffic will clear up. If you hit it wrong it can take 6 hours to do the same drive.
Figure the real traffic doesn't start until you hit LA. So since it's about 2 hours from Fresno to the bottom of the Grapevine figure you want to leave around 7am. This has you at the bottom of Grapevine at 9am. Los Angeles at 10am when people are at work, and 11 am as you're rolling through Orange County before the lunch traffic starts.
Or if you don't mind night driving leave Fresno at 4:30pm. Bottom of the Grapevine at 6:30pm, LA at 7:30pm when most are home eating dinner, and 8:30 through Orange County.
Figure about another 45 minutes to an hour from Southern Orange County to Pendleton.
There's just not much you can do to shorten the trip beyond 3 hours. But if you don't think about the basic commuter hours in a large city you can easily double your travel time.
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