Valve employee John McDonald said this with regards to the command: cl_forcepreload 1 being a bad command to use:
"Ahh, cl_forcepreload 1. Or as I like to call it "cl_massive_hitches_at_surprising_times 1"
We removed this from TF2 because it causes exactly the behavior that the OP is seeing. You almost definitely do not want this var set, ever ever ever."
"Whether we should force preloading model and texture information to video memory at the beginning of a level. Makes level loads longer, but can reduce stuttering caused by loading information on the fly"