1994 Chevy Caprice lack of power and burn gas

Engine Mechanical problem
1994 Chevy Caprice V8 Two Wheel Drive Automatic 140k miles

my 1994 chevy caprice 4.3 v.8 have lack of the power it used to have and burn a lot of gas, I had a complete tune-up( changed spark plugs and wires, cap rotor, oil, gas, air filters, pcv, throttle position sensor, temp sensor, gas regulator, egr valve, idle air control valve, trans filter. Trans diagnostic it was fine. Did a compression test, it was fine, check the injector they were fine, checked the fuel pressure that was fine, check the cats they were fine. Cleaned the mass flow sensor, and cleaned the throttle body to intake)And put it on the diagnostic machine and no other codes showed up, but my car is the same from before I started. What im I missing whatelse can I do to get my car back running good like before? My name is william @ 7737193229 or wbwilldeal@yahoo. Com