When I’m cruising on the highway or main road in 4th gear and I let off the gas, there's a small thud, and then again when I reapply gas. I am not sure if this is a problem or if it is

 

Not sure why the whole text was not posted previously. ----->

When I’m cruising on the highway or main road in 4th gear (determined by using Sport Shift) and I let off the gas, there's a small thud, and then again when I reapply gas. I am wondering if this is a problem or is it common for a TSX? Could it be the torque converter locking up or the DBW system? My car has an automatic transmission and only 29k miles so I am hoping this is not a transmission problem.

 

It sounds like there's potentially a loose or worn motor or transmission mount. If any of those, it's likely the front or rear engine mount.
It also could be one of the axles. Do you get any vibration when accelerating (and even moreso when accelerating up a hill)? If you get off of the gas, does this vibration stop?

 

I don't really have any vibration. It is more of a thud that you can feel when accelerating. If I just tap the pedal the RPMs jump a tiny bit and then decrease again almost instantly, which seems to cause the thud. I must ease on to the pedal very slowly to avoid this.

 

I'm not sure about if its the AT as I drive a 6MT, but it might be the DBW - these cars are known to be really touchy when just getting on or off the throttle.

 

Thanks, I hope that's all it is.