This is a very common problem with the 2003 chev Trailblazer. It's a poor design in my opinion that the #2 and #3 coils are deprived of air because of the design of the engine and the air breather covers. I have had to replace this same coil on numerous vehicles of this year, make, model and engine size.
Another common problem is the fan clutch locking up causing the vehicle to lose power and sound like an airplane taking off. If you have this type of vehicle and a similar problem, save yourself some time of diagnostics and taking it to a mechanic, just watch this video and change the parts yourself. Your will save several hundred dollars.
If you live in the metairie or New Orleans area and you need service on your vehicle, you can call me or go to my website and sign up for a repair at www.jakesmobileautorepair@gmail.com or call 504-723-2996.
Also check out my other video's and tips of the day on my youtube channel. click the link below
www.youtube.com/c/jakesmobileauto