There is a possibility that a separated motor mount may allow the engine to lift, which may affect the throttle linkage, momentarily increasing throttle, possibly to full throttle.
Engine & cooling
GMC P Series Engine problems by year
0 complaints filed with NHTSA about the GMC P Series's engine & cooling. Stalling, loss of power, oil consumption, overheating, head gaskets, timing chains and engine failure.
Source: U.S. National Highway Traffic Safety Administration (NHTSA) complaints and recalls, checked daily. Complaints are owners' own reports and are not verified. How we use the data