If the Mexican government is okay with this, the US government has no restrictions against this. However, always use your US passport to enter the US.
(213) 394-4554 x0 Mr. Shusterman is a former INS Trial Attorney (1976-82) with over 35 years of immigration experience. His response to your question is general in nature, as not all the facts are known to him. You should retain an attorney experienced in immigration law to review all the facts in your case in order to receive advice specific to your case. Mr. Shusterman's statement above does not create an attorney/client relationship.
Agree with Mr. Shusterman and just to add to it, these support what he says:
http://travel.state.gov/travel/cis_pa_tw/cis/cis_970.html (section regarding "Dual Nationality")
I agree with my colleagues. And yes, always enter the United States with your American passport and be truthful upon entry.
The answer offered here is purely informational and does not create an attorney-client relationship. This answer is not to be construed as legal advice.