first thing in the morning going down the street hit the gas it will spin the tires. after normal operating temp car falls down. taking off from a stop sign it acts like its running out of gas just lays down no power. 99 3.8L non turbo. parts replaced fuel pump and filter unkown miles on that . plug wires plugs air filter new tps. has different mass air flow sensor not a new one . did the same thing with the old one to. forgot no check engine light

Just so we don't repeat anything that you have replaced already......
How old is the O2 sensor?

When you take off from a stop do you notice any hissing sound coming from your cat converter?

A bad O2 sensor would decrease power and a plugged cat would also.

But since you said it loses power after its warmed up then it could also be a IAC sensor.( Idle Air Control Valve )

IAC sensor will affect the way the motor runs when its going bad.

Do a quick test the next time it acts up. Pop the hood and tap on the IAC sensor to see if engine power returns for a sort while.

Look for the sensor on your throttle body that looks like this where it plugs into the wire harness to find it:


What brand of fuel pump did you have put in?

The only reason I ask is because a bad fuel pump would also decrease power when its warmed up as well.

Have you checked your fuel pressure when the motor acts up?

o2 sensor not sure how old. no hissing niose from cat. iac motor looks like factory one. fuel pump gm / bosch pump in gm box. by the time i get home from when it does it its running ok but not like in the morning. wish i could get a cel then might have some direction to look. how nuts is that want a cel

Its tough to test this sensor but you could try going to your local auto salvage yard and pulling one from there and swapping out your IAC with that one to see if things change for the better.

Some have tried just taking out the sensor and cleaning it with break clean. The plunger inside does get all carboned up. Cleaning may be a long shot but might work until you can buy another one.

Not nuts at all. Have a trusted friend ride with that has a cellphone.
PM me if you want to do that, and I'll call you or have them call me sometime.

got a new iac at work going to put it on later . will let you all know if this is it hope so .

me to!

-Todd

put on new iac ran great. now the vacuum falls off going up a hill dont have to be steep either. with the ac on and blow through the deffrost vent. after 40 min ride back to same old thing turned off highway went to make my turn and flat like an old style carb would lay down . starting to make me crazy

Change the fuel filter next.

my guess is either that pump is either crap or your fuel guage is screwing with you.... here what happened to me one time
I was around half a tank until i hit the ramp towards the highway, and it decides to cut out!! after pulling to the side it kicks back in and im off. The ramp was a downwards right slope, realized that my fuel guage was *****n with me so now i keep her full