U7170 Line Pressure

[Excursionist]

I have an 2002 7.3 liter Excursion. What does the option "shift kit" in tuning do. Is it safe to use it? I have had transducer and solenoid work done to increase my line pressure over stock values.
Also, shifting seems sketchy with the r19dz tune. Seems to down shift a lot more than before. After having been in overdrive traveling 50 and then slowing to around 40, it sometimes shifts to 2nd for just a moment then back to drive without stepping on the throttle. This is on the 100 hp tune. Shouldn't there be sufficient hp to not down shift 2 gears? Don't remember this problem with the original tune files. 60 hp tune is weak and shifting is soft and fuel mileage is not as good as the 100 hp, yet it is the "economy" tune.
Is it possible to customize my own tuning as far as mph shifting, rev limit, top speed, fuel, tire size, etc. ?