I-140 Approved and Changing the Employers

[ramoji35]

I am working for Company A and have my I-140 & PERM approved with them. Now my direct vendor Company B wants to Hire me. My H1B Cap Out Date is Sep 2013 and PD date is Dec 2010

Questions

1)Is this a Good decision to change the Employers?

2)Can i retain the PD Date after changing the Employers?

3)Is it necessary for Company B to file for PERM and I-140 again? (Company A is willing to retain my I-140)

4) Can Company B file the I-485 Directly with approved I-140 from Company A?

Please Advice !!!!!