After the Searles tunnel caught fire in 1981, SP relaid the old summit route. I learned about it from the Ted Benson and Richard Steinheimer photo essay in August 1983 Trains.
Found a photo on Ebay of a loaded train climbing the shoo-fly in 1981.
A post on Trainorders says the grade was 3.67 percent.
Ebay item, not mine: [www.ebay.com