Did they do all 3 IMGs or just one? If not all of them you could be in for a repeat of this problem. Since you are not getting any symptoms like you did before I will assume this is not your problem though.

If the fuel filter was compromised enough to effect your milege, like I noted before you would very likely feel the vehicle stumble at speed and when accelerating heavily. So I don't think this is your problem. Still if you haven't changed it lately, it would be a good idea to change it now in any event.

My parts manual shows that ALL 4 oxygen sensors are the same. Only change is that different year 97+ Troopers take different sensors but each model takes 4 of the same sensor. You may want to call another parts store and get their take. Could be Bosch/Isuzu has susequently speced different plugs since my manual came out, but I doubt it.

To elaborate on my swap sensors suggestion. There are not a lot of posts about oxygen sensor problems on the newer Troopers. Thus, it seems that they are fairly robust. So I for one wouldn't assume one failed and automatically buy a new one and hope this fixed the problem. I would do the noted testing. Then again if you did buy a new sensor, and it didn't fix the problem, you would have a spare you could likely use in the future.

Lastly, any chance your area converted to low pollution gas about the time your mileage took a hit? Typically low pollution gas is less dense and while you get about the same miles per pound of fuel you get a lower miles per gallon. That could explain some of the mileage hit.