Loss of MPG?

I can't tell if you are saying the engine is misfiring or not, can you take a quick video of the engine running I can tell right away what is wrong. Also do you have any codes? You can get a code scanner from Amazon for about $20.00.

Here is a guide/video to show you how:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Here is a scanner link:

https://amzn.to/3Qi1SS6

This guide can help as well:

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Please go over these guides and report back.

Idles perfect, no misfires unless driving at slower speeds and you usually feel it when you let off the gas and it's jerks a little a couple of times.

Any codes? most of the time when this happens is because the MAF sensor is off but not enough to trigger a code. Here is the location so you can check it out and replace the sensor to see what happens.