That part of I90 is all of 3000' max elevation, and a max grade of 4% from Seattle to vantage going east out of gorge, then you are in the 5-6% range, Still under 3000' elevation! You have only lost at best 10% hp in a natural aspirated motor.
As other have said, let it rev! Even a diesel on these grades will be in the 70-80% of its rpm if at max load, and slowing down!
Worst grade out of seattle per say, is the grade to HWY 18 from Preston, then the last 100-200 yds after exit 51, to the actual summit. The rest is not too bad.
Marty
