Go around the pass by taking the 78 out of Ramona, then north (left) on SR-79 at Santa Ysabel, then right onto S-2, then left onto S-22 into Borrego Springs. Then the only big hill you have to worry about is the Montezuma Grade past Ranchita into Borrego. You also avoid all those twisty tight turns around Julian, which is no fun with a long vehicle/trailer combo.
You live in Santucky or San Diego? If you live in north San Diego (Mira Mesa / Poway / Scripps Ranch areas) then take Scripps/Poway Parkway up the hill to SR-67, then up the hill to Ramona. Its a steep grade, but only a few miles long. I drove the Explorer up that many times towing a 2500 pound trailer, and now I drive the 16,000 pound RV pulling the Explorer up same hill.