1999 Blazer ,no power on hills. 90,000 miles. What could be the problem.
Bad plugs and/or bad plug wires.
A compression test may show a problem.
What is the maintenance record of this vehicle?
Did you have the major 90k service done?
If not, you need to begin with essential maintenance before you try to start “cherry-picking” items to replace.
Check fuel filter and fuel pressure
I agree, and take it to a mechanic to get a compression/leakdown test. Also, did this “problem” happen overnight?