My truck makes a shhhh sound when I accelerate the air pedal.?

sounds like the cat converter is clogged. have the back pressure checked to verify

Roy

Did you check for trouble codes? Is the Malfunction Indicator Light showing?
Noise described seems to indicate a leak somewhere or clogging in exhaust system.

Roy yes it was checked, also, no cel comes on.

how was it checked?? what was the back pressure measurement??

Roy

I saw him put his hand over tail pipe.

thats not a test. it can still pass enough exhaust to feel it but not let the engine breathe.

thats why you need to measure the back pressure.

Roy

@ Roy I just had my cat converter installed a month ago my engine is good, it never blow black smoke out the tail pipe also, thank you for taking the time to help me with this problem.

sounds like a gross vacuum leak actually , something intake side or brake booster. those are the biggest lines you have in the system ( 1/4 ) some larger .. especially if its leaking to the booster that will cause a whole host of issues. if vacuum is dropping in the system it also could be shutting down the fuel pressure regulator which would allow more fuel into the rail under hard acceleration ..

I found out it is the EXHAUST manifold flange gasket. May I ask will this cause all these symptoms?

Yes, exhaust leaks can cause performance related issues. Have it rectified first.

check the vacuum line going into the truck. It is by the brake booster. One side goes to the engine and the other to a t with one part going into the firewall. The vacuum line works the heater control. The other side is plugged into a caninster inside the drivers side fender.