I'm in Ridgecrest and make that trip often....tomorrow in fact. From the turn off of 14 onto 178 the grade is gradual with most of it about 4% to 5% with a short stretch just as you reach the top of 6%. However, just over the crest, there is a 7% downgrade with a sharp horseshoe curve that you should slow to about 15mph. After that, there is again a gradual downgrade for about 10 miles until you get down in the valley.
If you are indeed going to the town of Kernville, the turn off of 178 is a couple of miles before you get to South Lake. This road is just fine for you but does have a couple of 35mph curves.
If you are going to Isabella, just stay on 178.
Hope this helps
Ron