Engines are air pumps... The easier the air flows in and out the more power you can make...
A good intake, (insulated if possible, silicone hoses), and good flowing exhaust, (insulated if possible, exhaust ceramic coatings in and outside) are a must... Then you can do performance cams with better springs, and a performance valve job... Then you finish the job with a Dyno Tune.
Together these parts will yield some power grains...
Remember Peak Horsepower is NOT your best goal. You are NOT going to brake a speed record on a big SUV... I would want a smooth power band with good torque at lower RPMS. This is where your SUV engine lives most of the time... Good acceleration to a cruising speed, more torque gives you just that.
If the horsepower increases great! How often will you be doing triple digits in your search of top speed???