1996 Volvo 850 Not shifting into low when I stop the car

Transmission problem
1996 Volvo 850 Front Wheel Drive Automatic 160, 00 miles

Approx. Six months ago I had the PNP switch replaced because (i) the car would always start out in high gear and (ii) an orange-colored arrow on the dashboard was always blinking. Based upon my internet reseach, I had concluded that the PNP switch was bad; the dealer confirmed my conclusion; so, I had the PNP switch replaced.

Last week the car, when hot (but not when cold), began not down-shifting infrequently when I came to a stop. The problem is most infrequent; there is no flashing arrow displayed; and if I quickly, momentariily and forcefully depress the gas pedal for a second or so, the car will most of the time immediately downshift into low gear, and all is fine (prioir to replacing the PNP swith months ago, this "tactic" did not result in the car's down-shifting).

I do note that the trans. Fluid, when hot, does go a little above the "FULL" mark on the trans. Dip stick. I had the fluid replaced approx. Four months ago, but this infrequent problem (car will not always downshift when the car is hot) just began last week.

Help, please.

Thank you.