hi all, i have a 98 tahoe 5.7 thatlooses power after half throttle, it has been this way to some degree or another since i bought the truck. ive kept up on regular service, air filter is clean and i clean the mass air sensor every oil change and replace the fuel filter every other oil change. i suspect the mass air sensor because after the first time i cleaned it the power really picked up but soon went back down, but for $150 i'm not really confident that thats it, thanks

 

I'm guessing you meant that you change your "air" filter every other oil change and not fuel filter.Are there any codes setting?
I had a similar issue on my 97 where a piece of the foam on the air filter came off and got sucked up to the MAF sensor and caused loss of power stumbling becasue the engine could not breath at highway speeds. It was blind luck that I found it becasue it was happending right after I did a tune up.
I'd check for:
codes
fuel pressure
clear air flow up to throttle body make sure nothing ever got sucked up into the breather snorkle
cracked distributor housing
crossfiring plug wires
try running some carb cleaner down the TB
a few bottles of injector cleaner thru the tank
other possibilities are:
throttle position sensor
crank shaft / cam shaft position sensors
check for any wiring that may be too close to the exhust manifolds, I had a harness come loose and started melting the wires and would only act up once it got hot from the exhust manifold.
Just some of my ideas to check....good luck, hopfully someone else hassome goodinput

 

Agree with in2pro. Recommend Techron FI cleaner.