2009 Ford Escape w/ 5 speed: Intermittent stiff gear shift

Car has about 199,000 miles on it, transmission was rebuilt around 150,000 along with a new clutch. Haven’t had any issues until recently. When winter came along I noticed when the car was sitting for a while (overnight) the gear shift was stiff and hard to engage into gears. After letting the car warm up a bit this went away so I didn’t mind it too much because I wanted to warm the car up anyway so I don’t freeze my ass off. However, in the past week or so, I have been having similar symptoms after driving for an extended period of time, such as the tail end of my hour commute to work. For the first 15-30 minutes it would be smooth as silk but then as the transmission got hotter (I guess?) it would start getting stiff. Not so much getting into gear but just moving the gear shift itself. It is more of a pain to move it horizontally than vertically, meaning shifting from 1st to 2nd or 3rd to 4th was perfectly fine but going from 2nd to 3rd or 4th to 5th is a pain. Pretty much any horizontal movement. It does not change if I turn the car off either, still stiff if the car has been running for a long time. I tried changing the transmission fluid, which was dirty and low, and made sure to put in the proper amount of Ford spec fluid, 75w90 gear oil. My first commute after that was still the same, stiff gear shift towards the end of the drive. On my way back home it did feel better but still not quite as smooth as when the transmission is cool. Any thoughts? Should I just keep driving it to let the oil work its way through the transmission more? Would the GM Syncromesh be worth a shot?