GM-GMC: 2000 Chevy Silverado losing horsepower, mass air flow sensor, mass air flow

Question
I have a 2000 Chevy Silverado with 120000 miles on it.  At about 100000 it started losing horsepower on the road and taking longer to accelerate.  Now, at 120000, it is taking 2 to 3 min for me to get it up to 65 mph.  Yesterday, while driving on a turnpike, my cruise control couldn't keep the truck at 75 mph on even the slightest incline.  It would drop to 70 mph and are sharp hills it would even go as low as 60 mph.  What do you think is causing my truck to lose horsepower and acceleration? (my fuel pump went out about 5000 miles ago and was replaced.)

Answer
There are so many things that can cause a condition like that.  Plugged exhaust, transmission problems, plugged air filter, poor fuel pressure, mass air flow sensor etc etc etc.  My recommendation would be to take it to a garage that you trust.  Go for a drive with the mechanic and get his opinion on what course of action to take.  If you want a blind guess, I would say check the exhaust back pressure for a possible partially plugged exhaust system.
Hope this helps