With kidney function tests showing renal problems (or failure) I would have to say it is time for an internist to investigate the case more deeply.
Did your dog show these symptoms immediately during the pet food recall time (over 2 years ago now) or did these signs just show up??
Other treatments are available, but before going into specifics here, I would highly recommend you get to a specialist for proper investigations and diagnosis. Only then can you treat specifically.
One of our own Med Help veterinarians is in Houston and I would highly recommend you give her a call. You will LOVE her. Dr. Lori Teller . Here is her MedHelp Profile. Please call her. Meyerland Animal Clinic
713.723.8612
4995 West Bellfort
Houston - TX
Here is her MedHelp Profile.
http://www.medhelp.org/doctor_profiles/show/945849