I have a 98 k2500 5.7, okay well a couple months ago my truck would run really weird like after I got of the high way or even drive it a lot one day. then out of know where it just stopped and then I noticed I had an exhaust leak where the doughnut seals the manifold to the down pipe wasn't seated right so I bought a new doughnut and fixed the leak but I noticed that it is running weird again! if anyone has had the same problem could you please help me out thank you!!

 

Could you describe what weird running is. What is it actually doing?

 

Well after it running it for along time like long drives it will start to loss power in the gas peddle and the exhaust sounds wierd like somthing is cloged up but my cat has been gutted already I was maybe thinking I have a bad coolant temp sensor but I don't know if that would cause something to run like it's not running on all 8 cylinders

 

And I also get a really bad rough idle starts to shake

 

With this crappy gas you nead to keep an eye on your throttle body, you wont believe how nasty dirty it gets.

 

sounds like you need a tune up. plugs, wires, cap, rotor, fuel filter, etc.