do your bench pressing first always. The majority of growth stimulation comes from the heavy compound movements such as the bench or a squat. In fact, at 137 lbs you could completely skip tricep-specific excercises and your triceps will growth and virtually the same ratewhether you did skull crushers or not.
Isolation excercises should always take a back seat to te compound movements.
And why are you doing decline bench first? Or at all for that matter? Just do flat and incline presing. Both dumbbells and barbell.