Ok First off, I got a 99 Silverado 5.3L w/ ~75000miles on it. Ok so just recently When I'm drivin' round messin' around and get on it, it runs fine till about 4500k and slows way the f#$% down and by 5k its just takin a dump and hardly gets(on both shifts 1-2 and 2-3) to get to the shift point and shift(like when I punch it, it puts you back in the seat a little bit then around 4500k you will lunge foward a little because it slows down so much)and when it does shift it sounds like s#!t the sound reminds me of someone hawking a fatty loogy. This has been going on for about a month and at first I thought it was because I was low on gas put my theory was proved wrong when I filled it up to the top w/93 octane about a week ago and it keeps on doing it. Spark plugs, Coilovers and wires changed less than 5k ago. So the only thing I think it could be is my fuel pump or some other fuel related part is crappin' out. Anybody know or might know what it could be? Feel free to ask any questions to help me figure whats goin on. Thanks any help is GREATLY appreciated!

 

How long ago did you last change your fuel filter?

 

yep.. fuel filter or pump...

no codes?

 

sounds like your havin the same problems i was having, mine was leaning out in the high R's up to 15-to 16:1 afr and it was just fallin on its face, first change your fuel filter and if that dont do it pull your injectors out and clean them , had a bunch of trash in mine and it helped it out alot.. i had to do some more tuning to get the afr corrected, its pretty easy to pull them out..it took me about 45 mins to pull em clean em and stick them back in. hope some of this helps

 

changed fuel filter <1000 miles ago, no codes, just starts crappin' out around 4500rpm, will check out injectors this weekend, How do you clean them out and what with?

 

How about those converters, plugged cats act that way.

 

I'm guttin' cats when my o2 sims arrive.

 

Get a can of SeaFoam and run though about half a tank. That will clean the injectors.

Change the fuel filter again, just to rule that out. If that's not it, try the fuel pressure regulator.

I pump usually works or doesn't. Very seldom will one just not keep up like it should. They will usually go completely out.

 

Will try all this out today.

 

Do you have any logging software or a scan tool so you can check the data when the problem occurs? If the fuel treatments don't do the trick, you may have a problem where a sensor is giving incorrect information under the conditions when the problem occurs...if it's within parameters, it will still run, just not throw any codes.

Also, did you try un-installing the HPPIII programming (listed in your sig), just to see if there was any difference? (I like to eliminate the aftermarket variables first whenever possible)