davemurray

I have a 1989 5.0 manual GT that's been hold into my garage for a couple of years, it has 145,000 miles on it, I've replaced the fuel system completely from the fuel pump, filter, lines, relay etc. Here's the problem, it lacks of responsiveness, I've heard everything from bad o2 sensors to worn heads, the car sounds tired to me.
Do I need to rebuild the engine?
I really want to recover the huge amount of power that has been lost during the years.
Any help would be greatly apreciated.