having problems with my 1999 1500 5.9. shifts out great idles great but when you take off or punch the gas when its up to speed it just falls on its face. need help.

 

We need more information. stock gearing/larger tires ?, has the plenum been fixed ?, when was the last time it had a complete tune up ?, how many miles on the engine ?.

 

180,000 plenum has not been fixed no sign that it needs it. 3.55 ratio stock tires. plugs and wires were changed about 1500 miles ago. check engine light flashed on and off for a few seconds the other day when accelerating at driving speed. code was for a cylinder 3 missfire havent got it to come back on. pulled the plug no sign of fowling. or anyother contaminents. compression was at 135psi. anything else that might help?

 

cat back straight pipe. iv been reading alot on 02 sensors and cats. thinking original cats from 180,000 ago could be the culprit.

 

180,000 miles on the original plenum gasket, I can just about guaranty you that its bad and needs to be replaced.


From what I`ve read these engines do need a little back pressure in the exhaust to run properly, so the straight pipe could be killing some of the bottom end power.


If the 02 sensors in your truck have more than 80.000 miles on them, or they are the original ones, they need to be replaced.


180,000 miles on the original cat, it should be replaced also

 

180K, your cat is toast, even a new cat kills power, ditch the cat and get a muffler.

 

Ditch the cat and get a muffler?? Depending on where you live, you cant just ditch the cat.

 

What kind of spark plug you use?

 

Get a magnaflow cat!
http://www.magnaflow.com/02converters.asp

 

Running without a cat is illegal in all 57 (Obama) states, but judging by his post/issues/mileage I doubt if he has to pass local emissions.