took a gravity reading today at the end of the transfer from the kettle and there was quite a bit of trub in the cylinder, like the whole flip'n tube. so would the trub hold the hydrometer up and give a false reading?
If the trub is actually physically holding the hydrometer up, preventing it from moving down, then unambiguously: yes, the trub will render your hydrometer reading useless.
If, on the other hand, the trub is suspended in the liquid, it is a mixed bag. Suspended solids will impact a hydrometer reading, but for brewers it is usually very minimal. The only actual measurements I've seen have put the effect at well below even a single point of gravity (thousandths digit on SG scale), though it is conceivable that the effect is more significant in very trub-heavy samples. Still, it's hard to imagine that we'd see an effect of more than a couple of points.