Norm,
Why don't you have a friend pretend to be a hiring manager and call you previous employers to see what they are saying. I've know some recruiters do this to make sure only the best references are presented to their clients. It might help to know if they are just giving you a so-so recommendation vs. out-right lying about your work performance. Just keep in mind that anything less than a glowing recommendation is enough to kill the hiring process IMHO, especially in the current economic climate where most job openings are innudated with resumes.