A hesitation between 1500-2000 rpm?

Did you ever do the suggested ECU reset via the battery disconnect procedure?

Perhaps you should take the car back to Mr Lube, mention the hesitation, and ask them to inspect under the car to see if they forgot to reconnect something, like a connector to some sensor. If any place offers a free inspection (or in combo with something that's cheap, like tire rotation, battery test, etc), take it in and mention you'd like them to carefully check around the tranny to check for leaks, if there is evidence of a tranny lube flush, disconnected connectors or broken wires, or anything else under there that is not right. At either place, have them check the vacuum hoses. I've had old ones get spongy or split and someone working around the engine could disrupt them enough to cause a vacuum leak. If the hoses are really old then they should get replaced.

Did Mr Lube do any other maintenance, like replace the air filter? If so, check the housing is clamped down tight so air doesn't come in that way. Even if they didn't replace the air filter, they might've checked it to see its condition and perhaps recommend changing it. Some Subies are tough to get at the housing, open, and then get it closed properly.

Don't in which hemisphere you live. In mine, it's summer which means winter in the other hemisphere (at the same or greater distance from the equator). If it is winter where you are, could be the air is getting routed up past the exhaust manifold to preheat it instead of the larger tubing normally used. I had a carburetor shop working on my nearly blueprinted Mustang for a couple hours trying to get rid of a hestitation on acceleration. They kept trying to adjust the jets and springs until I asked about the heated air intake which are much smaller tubes than the ram inflow path. Unplugged the vacuum hoses to prevent the flap from moving so the cold winter air only came through the front intake tubes. Hestitation gone. The heated air intake tubes were far smaller in diameter and couldn't deliver the airflow rate under hard acceleration. Never had an icing problem in the carb so left the control disconnected. Yeah, I know you don't have a carb. The point is that there could be a redirection of airflow during cold weather or other cold-weather components involved and it happened to get cold where you are.

I also had a car that would hestitate in cool damp weather. One cause (there were another but not applicable to your car) was old spark plug wires. Ignition/timing testing should find that cause. I replaced the spark plug wire harness (and changing to a vented distributor cap) and problem eliminated. Don't know if Mr Lube yanks off the cables to check the spark plugs. Not seating them correctly means a bad connection. Not using dielectic grease means rain or humidity can affect the connection. When the lube jockeys get under the hood, they can make screwups some of which may be accidental.

Wrong. A tranny flush is not like a simple engine oil change. Talking to the mechanic at the shop can tell you if they how to do it right. Tranny shops love how many lube shops do it wrong: more tranny jobs.

Just because you don't like the candidate for cause doesn't mean it isn't a valid candidate. It's an answer that you don't like because it means having the car inspected, interrogating the staff at Mr Lube to see exactly what they claimed they did (meaning you have to educate yourself before questioning them), and possibly having the tranny oil

*exchange* done again but at a different shop with better equipment, better use of the equipment, and better expertise.

Yes, we realize that you don't want to even consider that you threw away money on a job badly performed. But it happens. As shown in a linked video, that they charged you $200 doesn't mean they did the job correctly and perhaps not at all. You can see my other suggestions in another reply but they don't obviate a bad tranny change as a cause. My other suggestions are less pricey but if nothing else works then you might have to focus back on the tranny service (and get the staff at Mr Lube describe exactly what is that "service").

The hesitation is almost like you're lugging the engine, like in a manual transmission. But of course, this is an auto, so how can you lug an engine if you're on a straight level ground with just normal amount of cargo and passenger weights inside? It's just a light lugging sensation though, at these RPM's.

Now, interesting development just happened earlier today, seems to have fixed the problem. I'd been having a problem with the warning light that came on the dash for the past few months, the "Rear Differential Temperature" light had come on. I was told that 99% of the time that this light doesn't actually mean that there is anything actually wrong with the rear diff, it's usually some corrosion on the wire leading to the sensor in the diff. That's what it turned out to be this time too. I hadn't mentioned this issue, as I was scheduled to have it looked at anyway, and it didn't seem related to the engine hesitation issue, it seemed like a separate issue. Now I'm thinking maybe when the Rear Diff Temp light came on, maybe the engine management system was trying to reduce the power going to the rear diff?

Yousuf Khan

You gotta tell the whole story Yousuf. If there os a warning light involved, ALWAYS rule that out first!! Powere was likely being disconnected from the rear dif - which WOULD cause a surge sensation.