Crumb rubber (CR) from used tires is widely employed to modify asphalt, but it faces challenges regarding compatibility, workability, and performance after aging. This study analyzes the effects of KH-151-treated CR on CR-modified asphalt (CRMA) and the effects of incorporating varying contents of waste transmission oil into untreated CRMA and steel slag into KH-151-treated CRMA on the physical properties of unaged binders and the thermo-rheological behavior of unaged, short-term aged, and long-term aged binders. The prepared binders were evaluated through traditional binder tests, fluorescence microscopy, Fourier transform infrared spectroscopy, multiple stress creep recovery, linear amplitude sweep, and low-temperature rheological tests. Incorporating WTO into untreated CRMA increased penetration by 10.5–21.2% and ductility by 17.7–30.2%, while reducing viscosity by 12.7–30.4% and softening point by 13.8–22.2%, which improved workability and low-temperature relaxation but reduced rutting resistance and fatigue life at lower strain, and yielded the highest fatigue life at higher strain, even after aging. KH-151-treated CR in CRMA increased penetration and ductility by 24.8% and 81.2%, respectively, and reduced viscosity and the softening-point difference by 55.0% and 86.7%, respectively, thereby improving workability, low-temperature flexibility, and storage stability, while also retarding the rate of increase of carbonyl and sulfoxide indices with aging, enhancing fatigue performance at higher strain, and maintaining low-temperature stresses lower than those in untreated CRMA. Incorporating 5–10% steel slag into KH-151-treated CRMA increased the softening point by 2.3–4.7% and viscosity by 7.8–26.2%, enhancing stiffness and rutting resistance, while causing only slight reductions in penetration by 0.98–2.14% and ductility by 3.4–5.7%, together with a slight reduction in cracking resistance at low temperature. The findings indicate that moderate WTO in untreated CRMA and steel slag in KH-151-treated CRMA can help to achieve desirable workability, rutting, fatigue, and low-temperature cracking performance in different pavement applications.