I have a '92 V6 and recently (6/21-7/21) got a new cat converter, tune up, starter and a/c compressor. After the starter and cat converter, it felt like it was straining. Took it back in and they said it was an unplugged nox sensor. After I got the A/C compressor, when I have the a/c on and I step on the gas, it feels like its straining, only worse than before. If I'm coasting or am going 30-35, it seem fine. The minute I put my foot on the gas to go 40 etc. I actually feel it in the floorboard! It's not a heavy vibrating, but I can feel like it's just straining. If I let up on the gas, the grrrrrr sound goes away. HELP! I got the a/c compressor at the dealer and the other stuff at a local shop. Not sure who I should take it back to.

 

Check for codes 1st.

 

Wouldn't be the starter. The cat isn't very restrictive, so shouldn't be that either. Are you sure they didn't give you a tune-down, instead of up? Maybe your ignition timing isn't set right, double check that. And it's natural for you to feel a noticeable drag when the A/C is on, especially with a little V6. The compressor is a huge power robber. Since you needed a new compressor, I can only figure that the old one wasn't working, not engaging, and not dragging the engine down? So you may be comparing apples to oranges there. When checking for the straining, make sure all of your heater/AC controls are turned off. With the lever in the defrost position, the A/C runs to remove cabin humidity.

 

It is possible something in the new converter became dislodged and is blocking the exhaust, causing excessive back pressure. This is not common, but is a possibility. I had something similar happen to one of my cars in the past. It is more likely a timing issue.