19.5's look undernourished on a 1.5 ton truck. 22.5's are the direct replacement for the original 20" tires. No matter what wheels and tires one uses, most original 20" tire fenders are narrow, so modern wheels, no matter what size, stick out.

There are factory full width fenders for GMC trucks, never seen them on Chevies. Hard to find, they are 25" wide at the back of the headlight bucket. I have seen two pair, pix for email address.

Ed

'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.