Burnt clutches and poor shifts are common issues with GM 8L45 and 8L90 transmissions. These issues can be caused by worn clutch control bores allowing valuable clutch apply fluid pressure to leak, reducing the force needed to apply the clutches. Reconditioning the bore and installing Sonnax oversized S1/S5 clutch control valve kit 154740-42K restores proper function.
Vacuum testing at the port(s) indicated fails to hold the recommended minimum in-Hg, or if wear is visually detected.
