I've been trying to dead lift heavier (up to 380), but seem to have reached a plateau...the biggest obstacles seem to be my grip strength (thinking of using straps) and pressure on the lower back. Is it time to use a belt? what are the drawbacks to using one? and should I just put it on when I get to the heavy sets?
I would advise against either straps or a belt. Your grip and lower back seem to be weak points; you want to work on strengthening them and these pieces of equipment do the opposite, taking pressure off. You'll end up with an even greater strength imbalance.
Instead, work around your plateau for a while and focus on techniques that will help these problem areas. A few suggestions:
Once you have your grip and lower back stronger, then you'll develop new weak points (quad strength, for example) and you can once again work on increasing that and increasing weight without equipment crutches.