hey i have a 98 gmc jimmy 4.3 vortec that has about 200k on it when you push the gas pedal all the way to the floor like when your passing someone it acts like its holding back and has no power like there is maybe a bad sensor or air or fuel issue i have been told could be o2 sensor just trying to get more info before i go putting alot of money into it any help would be great thanks.

 

Could be a plugged cat, shift solinoid, low or dirty trans fluid & filter, vacuum leak, over heating, mass air flow, fuel pressure issue.
Start by looking up the steps to diagnose those issues & search around in here for what others have posted in related issues.

 

When is the last time it had a tune up? Cleaned the MAF and EGR? I would start with a fuel pressure and leakdown test depending on your answere to the first 2 questions. May also be as simple as a plugged cat.

 

200k, please be aware of the plastic timing chain problem:

https://blazerforum.com/forum/2nd-ge...e-ideas-73291/

The plastic cover is warping, GM has a shim kit to get it back in place.

 

i just put new distributer,distributer cap,rotor button,plugs and wires and a new fuel pump about a year ago i got it hooked to a computer today they said bad o2 sensor but there is three or four of them which ones should i change first and how can i tell if the cat is clogged with out taking it to a garage and having a pressure test done thanks

 

the vehicle is sometimes hard to start on a cold start but once it is warm it fires right up it idles fine no miss in it at all. it does fine till you push gas pedal all the way to floor and jumps up to higher rpms and looses all power thanks

 

The hard cold start doesn't seem to be part of the issue with the loss of power IMO. If it revs up but doesn't go anywhere fast then it's in the trans. If it wasn't able to rev up without coughing, stuttering etc then you have engine issues like I've mentioned & others have.
A cold, hard start could be many things, old oil, IAT, MAF, EGR to bad bearings etc.

 

Sounds like an fuel issue. I had this problem and it was my fuel filter restricting fuel to the motor.

Remember it dont hurt to have a new filter any ways.

 

i bought the vehicle with about 70k on it and i have maintained it really good as far as fluid changes, filters and stuff like that. if you was to change the o2 sensors which ones would you start with? what kind of fuel pressure am i suppose to have when running?thanks for all your help so far.

 

You test the fuel pressure with the key on, engine off! It should be 60 to 65 and not go below 55 for 10 minutes. If you know someone who has a scan tool, you can check how active the o2 sensors are. They might be getting lazy but not bad enough to throw a CEL.