Can the 2020 GMC Sierra 1500 make a U-turn?

No. Needs more than 40 ft.

49.5ft curb to curb

Street width, feet

Street 40 feet curb to curb.

2020 GMC Sierra 1500 Base LB RWD. Top view, to scale.

2020 GMC Sierra 1500: turning circle by trim, 40 ft street
Trim	Circle, ft	Margin	One move
2WD Reg Cab 140"	44.7	-4.7 ft	No
Base LB RWD	49.5	-9.5 ft	No
Double Cab RWD	46.3	-6.3 ft	No
4WD Reg Cab 140"	44.7	-4.7 ft	No
Base LB 4WD	49.5	-9.5 ft	No
Crew Cab RWD	46.3	-6.3 ft	No
Crew Cab LB RWD	49.5	-9.5 ft	No
Double Cab 4WD	46.3	-6.3 ft	No
SLE Double Cab RWD	46.3	-6.3 ft	No
Crew Cab 4WD	46.3	-6.3 ft	No
Crew Cab LB 4WD	49.5	-9.5 ft	No
SLE Crew Cab RWD	46.3	-6.3 ft	No
Elevation Double Cab RWD	46.3	-6.3 ft	No
SLE Crew Cab LB RWD	49.5	-9.5 ft	No
SLE Double Cab 4WD	46.3	-6.3 ft	No
Elevation Crew Cab RWD	46.3	-6.3 ft	No
Elevation Crew Cab LB RWD	49.5	-9.5 ft	No
SLE Crew Cab 4WD	46.3	-6.3 ft	No
Elevation Double Cab 4WD	46.3	-6.3 ft	No
SLE Crew Cab LB 4WD	49.5	-9.5 ft	No
SLT Double Cab RWD	46.3	-6.3 ft	No
Elevation Crew Cab 4WD	46.3	-6.3 ft	No
Elevation Crew Cab LB 4WD	49.5	-9.5 ft	No
SLT Crew Cab RWD	46.3	-6.3 ft	No
SLT Crew Cab LB RWD	49.5	-9.5 ft	No
SLT Double Cab 4WD	46.3	-6.3 ft	No
SLT Crew Cab 4WD	46.3	-6.3 ft	No
SLT Crew Cab LB 4WD	49.5	-9.5 ft	No
AT4 Double Cab 4WD	46.3	-6.3 ft	No
AT4 Crew Cab 4WD	46.3	-6.3 ft	No
AT4 Crew Cab LB 4WD	49.5	-9.5 ft	No
Denali Crew Cab RWD	46.3	-6.3 ft	No
Denali Crew Cab LB RWD	49.5	-9.5 ft	No
Denali Crew Cab 4WD	46.3	-6.3 ft	No
Denali Crew Cab LB 4WD	49.5	-9.5 ft	No

What this cannot tell you

Curb-to-curb turning circle as listed.

Mirrors and overhang need more room.