I own a 2007 endeavor at 143,000km. I noticed the car shudders at about 40-60km then stops when I increase acceleration. The automatic gear selection is no longer smooth as i feel a tug when the gear shiftsBut when I shift to sports mode and shift to gear 2 @ 40km/hr, to gear 3 @ 60km/hr and to gear 4 @ 80km/hr this shuddering does not happen. I have also noticed increased fuel consumption and a funny smell from the exhaust as if something is not completely burnt.
i did a full scan and the only part that failed is the airflow meter. I wonder if this could be causing all these problems. Anyone with similar experience?

 

Is this RPM related? I had a similar problem. Turns out the exhaust flange went bad and caused the two halves between the flange to vibrate when I hit a certain RPM. Cost about me about $300 for the dealer to fix.

 

Its your automatic transmission fluid due for flush Honestly dont worry about it! it will not get better or worse.
my aunts 05 endeavor awd does this since she got it used at 130,000 miles its been 4 years! and it still hasnt gotten any better or worse.. true story too she always ignored it because of how well the car worked we all told her it would break but she always ignored us and we were wrong. it still shudders the exact same way as your describing even in sports mode but it has some good extra power. but her endeavor runs the same after 4 years this thing has 259,684 miles i was just in it today with her i had no idea a car can last so long.. she never even changes the oil just top ups when it gets loud enough.. the car is said to have lower mps compared to other cars for sale at the time but it is reasonable and i think thats just your case the needle goes down fast but it can go near red for a longgg time.

Our muffler looks pretty old and smells funny too but thats just age no worries the problem wont make that any worse ALSO if you begin to hear a metallic rattle anytime soon ( we did a few months into owning it with this issue) thats just an exhaust heat shield lose..
Trust me this car is amazing heres one example..

to fix the shudder take it to a mitsubishi dealer they told us the torque converter act up a bit if you dont change your transmission fluid with the problem mitsubishi brand one and that will possibly solve your problem 90% of the time but they seem common in these endeavors and some others too maybe if you ignore it long enough.. catch your problem quick if you want