If you have sport or track mode, those should help keep you in a lower gear a little better, but they will still try and shift up once you get off throttle a bit.
I pretty much always drive with the shifter in S due to this. If you keep it in D, the car's goal is pretty much to get to 10th gear as quick a possible. Other than that, using the paddles while in S will let you pick the gear and hold it there until you shift.
Yeah, in Normal mode, mine definitely locks in at 10th gear at too-low speeds and lugs a bit. It's been that way since I bought the car, and it remains true after I had my transmission fluid topped off, which fixed all of my other shifting issues.
I think it does the same in Sports/Sports+ modes, but it's quicker to downshift. But I can't remember off-hand (and I just got done driving the darn thing).
Also:
[1] Trans selector in Normal (D) mode:
After initial vehicle start up, when the Trans is in (D) and without driver intervention of touching the paddles, the trans is going to auto shift based on what it has adapated from learning the Driver’s driving habits and Ford’s mapping. The trans will hold the gear long enough as preprogrammed from Ford’s mapping and will auto down/up shift as needed based on that mapping AND the adapted Driver’s habits. The transmission will select the BEST and most OPTIMUM gear needed - it does NOT always shift like 1,2,3,4,5,6,7,8,9,10 nor does it downshift through 10 consecutive gears.... it could go 1,3,5 or if downshifting, go 9,7,5.... you get the idea.