My 2001 5.9 acted the same as yours. 60,000 miles at the time. Ended up being the plenum gasket underneath the intake which was fouling my precat o2 sensor making the truck pop and shake. Sometimes it would run fine. But it seamed like it was getting worse. I replaced the plenum, o2 sensor, gave the truck the normal plugs, wires, distributor and it ran better than I ever remembered.

You could probably just change the o2 sensor and it run good. But if that dang plenum is bad, it will go bad again.

 

Ok took the pre cat O2 Sensor off and drove it about two miles. Was alot better, but it still had just a minor hesitation. It didn't shake my truck like it usually does, just a minor hesitation. FYI, I put two bottles of fuel injector cleaner in the tank a day before I posted.

I'm thinking change the O2 Sensor and check Fuel pressure because of the minor hesitation I still have. Possible fuel filter change?

 

unfortunately our trucks dont have serviceable fuel filters, as they are affixed to the top of the fuel pump assembly, thanks to the all-mighty chrysler engineers that designed that, our cheapo made in china dashes, and the same ones who thought itd be smart to slap a stamped steel plate to an aluminum intake with a rubber gasket in between, hmmm... some engineers they got. i know 5 year old that know that steel and aluminum have different rates of expansion...

 

If it drives better with the O2 sensor out of the hole in the exhaust, better look real hard at the cat as well.

 

So how do you look at the cat without cutting it off? Sorry if its a dumb question, I'm not exactly a mechanic.

 

you can't really. here's a couple of ideas.
http://autos.yahoo.com/maintain/repa...ques083_0.html

based on your original post that the hesitation cleared up at 60 mph and higher RPM's, i'd guess your cat if not the problem. the typical symptom of a clogged cat is for it to idle ok, but not rev up beyond some fairly consistent rpm, say 2000 or 2500 or 3000.

O2 sensor problems generally arise only at normal operating temp. when the engine is cold, it runs off standard parameters (see open loop). when temps are normal, O2 is monitored (see closed loop).

do you have a check engine light on. check for codes by turning key on off on off on. watch odometer, it will end with p-done.

 

Codes are bad O2 Sensor and Large Evap Leak

 

^ you could have mentioned that earlier.

 

replace the faulty O2, bank 1 sensor 1 is pre-cat, bank 1 sensor 2 is post cat. more than likely your pre-cat is the faulty 1

 

Sorry, after everything I read, people were saying that those codes can come up with the smallest of problems, so I ignored them.

New development. I have an automatic, if I put it in 2nd it runs perfectly fine with the exception of the initial acceleration. Also, now when I idle its like clockwork, every two seconds or so, the motor stumbles.