I have a 2001 with the 5.9 and I've been experiencing this for a while now and it's drivig me crazy. my truck accelerates really poorly it feels like it has no power unless I floor it to accelerate. when I do accelerate I can hear like a hissing/whooshing noise coming from the engine (best I can explain it) also at about 45mph+ cruise in order to quickly accelerate I have to floor it and it will shoot up in rpms like I downshifted and it is not a smooth acceleration. from acceleration from a stop and up hills if I do not floor it it surges rpms but not down rpms instead it goes up rpms I can hear it from my exhhaust being loud it shoots up maybe 200rpms for a second snd drops back down. I've already replaced my tps and I really just want to know what's causing this hope it is not transmission problems. any advice appreciated

 

Have you read the plenum sticky?

 

yes and those symptoms dont sound like mine I am not burning oil and my truck runs fine at idle. it could be a million things im thinking clogged cat, clogged fuel filter, vaccum leak, bad map sensor and I'm just seeing if anyone knows for sure with all the symptoms I listed

 

Do you have wild vents? Sounds like a massive vacuum leak.

 

OP: Hang a vacuum gauge on the intake manifold and see what it says. Should be around 20"/Hg at idle (at or near sea level) with a rock steady gauge needle. To compensate for elevation, if needed, expect/accept a drop of about 1" per 1000' -- 15"/Hg is normal for my engine in my garage at 6350' above sea level.

 

Isn't a plenum leak a massive vacuum leak?

Remove the front O2 sensor and see if it runs better to find out if the cat is clogged. If the cat is clogged, you have or had a plenum issue.

 

Indeed, and that might in fact be the problem, but it might also be something simpler like a disconnected and wide open PCV hose, or a missing cap on a vacuum port, or a busted cruise control vacuum actuator, or a marmot riding on the fender well playing with the purge solenoid.

It's probably not a marmot. I'm just obsessive about troubleshooting and like to start at zero rather than making assumptions. It could be a marmot...

 

It does sound like a clogged cat, but there are many other reasons for a cat to clog than a leaking plenum.