I have an 01 monte ss 3.8 with 150k on it. In the last week or so lost power as in you floor and it will increase in rpms but won't go for a few seconds then takes off but not as fast as it used to. I check fuel pressure it was 10 psi, replaced fuel filter got me to 30 psi. Then the pressure regulator went out and replaced that. Was only at 40 psi after that. So I put a new fuel pump in and now I'm back in the 80-90 range. But still has no power. Has better then it had but still not the same as it used to. Also did a cylinder balance test and each cylinder dropped the idle around 200 rpm each. No dtcs or anything except traction control and abs because the left from Hub sensor is out. No rotten eggs smell either. Any suggestions? Also checked plugs and they looked fine, cleaned throttle body and idle air control

 

Just because you don't smell the rotten egg, doesn't mean it isn't the cat. You should get it back pressure tested.

 

I would say it's just because it's a Monte Carlo... but if you're even SLOWER than usual I agree with Mike, I would look into getting the pressure tested lol

 

We need pictures.. maybe it's the appearance causing it to be slow?

 

Also check your Trans fluid. If it is low or burned it can cause a loss in power due to slippage on take off or left turns.

 

He would definitely feel and hear errors with the trans though if that was the case, you would think at least

 

Definitely feel and hear a Hard Clunk! In 1st and 2nd gear!

 

Any way I can chek the cat without taking it to a shop to do the pressure test?

 

Drive it hard at night and then look underneath and see if it's glowing red, or take some temperature readings before and after the cat and see if there's a huge change