H1b: Expires on 02/13/2012
Priority Date: 09/29/2010
I-140 Approved: 05/23/2011
Category: EB2
485/EAD: cannot file due to retrogression

My employer(Company A) is giving me hard time to file H1B extension because of the billing rate issue with the client. My employer is not willing to provide I-140 approval notice but I do have I-140 case number.
1. Can I change to "employer B" without having I-140 approval notice but based on I-140 case number, assuming I don't receive the I-140 approval notice in next 2/3 weeks thru FOIA.
2. Also when I move to the new company(Company B) will I be able to file for a 3 yr extension as I have an approved I-140 of Company A
3. What is the best way to retain my old PD date when I move to a new company(Company B).