USPS United States Postal Service delayed delivery of valuable time sensitive official and business mail Internet

the second mail with printed postage sep 03 had a 'presorted first class' zip 75238.

inside was a valuable offer with 'expires september 10, 2010'.

The check was dated the 1st and post marked the 3rd. Normal.

You first say it was delivered on August 6th then the next sentence you say it was delivered August 11th. 

Which is it? 

Your post didn't indicate by what method the time sensitive material was sent to you.  Did it arrive via First Class mail, Certified Mail, or another method?

For time-sensitive mail, the postal service recommends the mail items be sent using Priority Mail or Express Mail.  Priority Mail has a delivery time of 2 - 3 days; Express Mail has a guaranteed overnight or 2nd day delivery date, though it is more expensive than Priority Mail.

I have frequently sent time sensitive mail items using Priority Mail flat rate envelopes or boxes, and have found the average delivery time is generally 2 days from the date the item is picked up from my home by the USPS.

As for the U.S. Treasury check...I doubt there is much that can be done on that issue, unless the check you referred to is for something like Social Security benefits or Veterans Disability compensation.  In the case of checks like those, they are normally sent to your local post office ahead of the delivery date which the issuing agency has specified.  The post office holds them until the delivery date indicated by the issuing agency.

Hope this might be of a little help.