Can the 2020 GMC Savana make a U-turn?

No. Needs more than 40 ft.

43.4ft curb to curb

Street width, feet

Street 40 feet curb to curb.

2020 GMC Savana Commercial Cutaway 3500 Van 139" RWD. Top view, to scale.

2020 GMC Savana: turning circle by trim, 40 ft street
Trim	Circle, ft	Margin	One move
Commercial Cutaway 3500 Van 139" RWD	43.4	-3.4 ft	No
Cargo Van RWD 2500 135"	49.2	-9.2 ft	No
Commercial Cutaway 3500 Van 159" RWD	54.5	-14.5 ft	No
Commercial Cutaway 3500 Van 177" RWD	54.5	-14.5 ft	No
Cargo Van RWD 2500 155"	54.5	-14.5 ft	No
Commercial Cutaway 4500 Van 159" RWD	54.5	-14.5 ft	No
Cargo Van RWD 3500 135"	49.2	-9.2 ft	No
Commercial Cutaway 4500 Van 177" RWD	54.5	-14.5 ft	No
Cargo Van RWD 3500 155"	54.5	-14.5 ft	No
LS 2500 RWD	54.5	-14.5 ft	No
Passenger RWD 2500 135" LS	49.2	-9.2 ft	No
Passenger RWD 2500 135" LT	49.2	-9.2 ft	No
LT 2500 RWD	54.5	-14.5 ft	No
Passenger RWD 3500 135" LS	49.2	-9.2 ft	No
Passenger RWD 3500 135" LT	49.2	-9.2 ft	No
LS 3500 RWD	54.5	-14.5 ft	No
Passenger RWD 3500 155" LS	54.5	-14.5 ft	No
Passenger RWD 3500 155" LT	54.5	-14.5 ft	No
LS 3500 Extended RWD	54.5	-14.5 ft	No
LT 3500 RWD	54.5	-14.5 ft	No
LT 3500 Extended RWD	54.5	-14.5 ft	No
2500 Cargo Extended RWD	54.5	-14.5 ft	No
2500 Cargo Regular RWD	54.5	-14.5 ft	No
2500 Passenger LS RWD	49.2	-9.2 ft	No
2500 Passenger LT RWD	49.2	-9.2 ft	No
3500 Cargo Extended RWD	54.5	-14.5 ft	No
3500 Cargo Regular RWD	54.5	-14.5 ft	No
3500 Passenger LS Extended RWD	54.5	-14.5 ft	No
3500 Passenger LS RWD	49.2	-9.2 ft	No
3500 Passenger LT Extended RWD	54.5	-14.5 ft	No
3500 Passenger LT RWD	49.2	-9.2 ft	No

What this cannot tell you

Curb-to-curb turning circle as listed.

Mirrors and overhang need more room.