Sport mode shift points

[TahoeM3]

Does anyone else find their car shifts from 1-2 too quickly in Sport even with M Mode on? I find that if I'm in S1 and go around a corner at an intersection and punch it, it will quickly shift to S2 even if it's only at 3500 rpm...kind of spoils my fun. I would put it in manual but the 1-2 upshift in manual is tough to hit right and usually ends up being a bit clumsy. Is there any other way to force it to hold S1 while taking a turn?

As an aside, I did a baseline VBox run stock. Keep in mind it's new...just past break-in, and I didn't use launch control, just power brake at 2500 rpm. Runs done mid-day in S. Florida in 90 degree heat and humidity (dew point of 73 gives me a density altitude of 2400+ ft despite actually being at around 0 ft altitude).

0-60 was 4.5 with 1 ft roll-out (more exact 4.46)
0-100 10.9
1/4 mile 12.93 @ 108.7

Not bad baseline runs, and it was very consistent. I know BMW engines aren't fully broken-in and loosened up until at least the 5000 mile point, so I'm sure there will be lots of improvement in time. The point of doing a run now was to see if there is any measurable difference with the regular tires that I will be putting on tomorrow.