Got drop foot 3 weeks ago, 1 wk ago started massive b12 doses. now i can lift it enough to walk almost normally -- could it be the b12?(also lots of pt)

Yes.: You've indicated you had your stomach removed which plays a role in B12 absorption. If your B12 levels were dangerously low on blood work it may have been the cause as well as other things like nerve compression. Talk to your doctor about this.

B-12 neuropathy: I would give more credit to the physical therapy in this case. B-12 deficiencies, when severe, can cause peripheral neuropathy. Despite this, to develop a severe enough problem to cause the loss of motor nerve function that would cause a foot drop would take a long time, and would be preceded by numerous other symptoms. Additionally, a vitamin deficiency would likely affect both legs/feet.