If you are plugging your coulters are not set properly and or your grasses are very tall. Often plowing is easier if a field is disced prior to plowing, and allowed to dry a bit.
Proper setup with the right tire spacing and plow positioning is critical for good plowing.
This is just my opinion developed from plowing with several tractors from an Allis WD, IH 400, 560, Ford 8000, IH 1066, 1086, then Magnum series 7110-7250's.
Draft control very seldom works well, when your tires spin you are actually putting less of a draft load on your tractor.
The later electronic computer controlled draft using lower arm sensors will work marginally, they are better when interfaced with the ground speed radar units.