Trouble shifting after new belt?

Just curious if anyone else has had trouble with shifting and transmission dragging after installing a new drive belt? The suburban 12 uses
a 5L style belt of 81" circumference (3/8" thick x 5/8" wide).
Trouble is it constantly drags on the motor pulley just enough that the tranny input was always turning even with the belt loose as a
goose (clutch/brake fully depressed).
I tried both a rubber fabric belt as well as a Kevlar fabric type-same results. I took off the motor pulley and buffed up the V groove-same
results.
After fretting a couple days over this, I came up with a "belt brake". I made up a couple of brass shoes to capture the top side of the drive
belt when the clutch is fully engaged. The upper shoe is fixed (bolts through a slot already punched in the frame). The bottom moving
shoe has a steel dowel to guide it to the upper shoe. It is attached to a 6" long piece of keystock which attaches to the existing
clutch linkage rod below.
Works like a charm
Thanks,
Joe K

I had the same problem with an ST-12. It got so bad I couldn't release the clutch when the belt was hot and the only way I could mow and not destroy all my downspouts was to rub parafin on the belt to reduce the friction. Then I discovered belt that were made for tractors and not industrial use. My local Ace hHardware store has belts with a low friction cover made just for clutch use and the problem is forever solved.

I kind of thought there must have been something different about the original belt. Its sort of unusual that these low friction belts
are not mentioned in the Mcmaster-Carr or MSC supply catalogs. It sure would have spared me a project!
Thanks,
Joe K