98 sierra 5.0, Hesitation and Misfiring Problems

I have a 1998 GMC Sierra with a 5.0. liter engine. The engine has 118,000 miles on it. My engine idles fine, however when I give it gas it seems to hesitate, bog down, and occassionally misfire. The codes that came up indicated low voltage from my o2 sensors, and misfiring. Since the problem first started I have changed my O2 sensors, plugs, dis cap and rotor, fuel filter,and cleaned my fuel injectors. I also had a fuel pressure test and vacume test done on it, and the mechanic said that everything was normal. Some days it runs better than others, but it still has the same problems. This has been going on for two months now and Im getting really tired of it!

Did your mechanic check the fuel pressure under load?

It could check out fine at idle, but fall on it's face under higher fuel flow demands. Also have him take a close look at the (TPS) throttle position sensor.

Just accouple ideas!

-Mike

Thanks, Ill give it whirl!