my father in law has a98 2wd chevy with a 305 vortec in it. the prblem is that whenever he gets into the gas it falls flat on the nose. the entire fuel system is replaced. as well as the whole exhaust and we did a tune up. yet it still does it. any suggestions???  

Well for starters, what in the fuel systems has actually been replaced??  

injectors, pump, filter, the tank, gas cap, and lines  

Does it run the same hot or cold and does it respond differently to part throttle than heavy throttle or how you step into it. Does it miss. cut out or is it just weak?  

it runs the same hot or cold. It does fine maybe a little sputter here and there, up until 60 or so. and then if you have to pass someone or jump into the throttle at all the truck just goes flat. the fuel fuelpressure is absolutely perfect. its not missing at all and it doesnt cut offwhen it happens, just falls flat  

I have a suggestion for you. Since this is a OBD2 truck, beg, borrow and buy a code reader that also can show real time data. The reason being is that you want to monitor ignition timing when problem happens. Might want to watch fuel pressure too. I suspect a problem with timing control here as it can cause a loss of power too.