Car missing/ running poor under heavy load?

Crankyster_01

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Just recently picked up a sn95 5.0 w/5 speed. Car starts and runs pretty good for the most part. When purchasing the car the previous owner had cut the exhaust right after the first cats suggesting they need beat out due to being stopped up possiable causing the issue the car is having. My issue is under moderatetly heavy acceleration the car acts like it hits a wall not really a miss just won’t go I can let off and resume normal throttle and she goes good. If I step on it wide open it backfires from the exhaust and sometimes it will take off and run good not often though. You can ease into the throttle very slowly until u reach wide open and it does good. Ive been through a bunch and have finally thrown a part at it I wasn’t sure about and it wasn’t the issue, I’m not one for wasting money on parts the vehicle does need and am at a loss, I’m right before bringing it somewhere and seeing if somebody else can figure it out. I’ve replaced the plugs and wires and replaced with good components, plugs gapped as required at I believe .54 whatever all data said. I ve tested the tfi multiple times like around 15 times and it passed every time at the auto parts store. I put on TDC and pulled and restabbed the dizzy and set timing to 13 btdc, I pulled the little gray thing when setting timing as required( replaced the dizzy today actually). I checked fuel pressure and found at 38 psi and 40 with regulator unplugged with no fuel present in the regulator. I checked for codes and found one code 556 for fuel pump failure, I checked the CCRM with a new unit to find the same results, I haven’t check fuel pressure when driving under hard acceleration to see what that does. I’ve checked for vacuum leaks and found that’s what was up with the a/c vents and it’s now fixed but no other vacuum issues. No other issues with the car everything works it’s just this darn acceleration issue I cannot drive the car how I desire ( like I stole it) anybody have any other suggestions I think I have covered everything I’ve done. I did remove the cats and installed an off-road x pipe and some magnaflow mufflers. I’m a diesel mechanic by trade and have been for 19 years this gasser is kickin my ass, and right before bringing to somebody to see if they can fix it.
 

Crankyster_01

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Forgot to mention I have cleaned the throttle body which was pretty bad and the tps with required cleaner.
 

RAU03MACH

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sounds almost like a mass air flow problem, just check it for shits and grins
 

Crankyster_01

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sounds almost like a mass air flow problem, just check it for shits and grins
I’ve removed and cleaned even though it looked fine, I’ve unplugged the MAF and started the car to find it then idles like crap.
 

RAU03MACH

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the cold air sensor is clean and has no oil or dirt around it if you remove it
 

07GtS197

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Could be a weak pump or bad regulator. Only a 2 psi jump with the vacuum hose off is not good.
 

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