...but only in 3-5 gear.

Reggie's (2008 clubman 6-speed regular) sweet spot is somewhere between 2500-3500 rpms. Always has been, but now he is starting to gently lug at anything close to 2000 in 3-5 gear, such going up a hill. It's not dramatic jerking, and probably no one but me would notice, but he does have 92,500 miles.

I shuld also say as per Arkansas weather, there is about a 20-30 degree difference between night and day here, and it got cold fast.

I was planning on changing his transmission fluid at 100k. Is this something I need to be worried about? Should I go ahead and change the fluid? I plan on driving this car until the wheels fall off...

 

Changing the fluid wouldn't hurt.

Does it feel like the car is shuddering at idle too?