Seafoam didn't work! When you replaced the egr valve a year ago did you see a bunch of black gunk down in holes the egr valve went into?

If not scratch that it could be a # possibilities but nothing for sure:
1.) Go to advance or autozone or anyone who will check the CEL light for free (if its on) get the codes and what they mean.
2.) fuel filter/fuel pump?
3.) tuneup (spark plugs, distributer cap, spark plug wires)? Also, how is that timing belt and serpentine belts replacement coming (not to good on my car as its going to cost me $715)?
4.) Also do you do the mandatory maintenance (air filter, oil, oil filter, etc...) every 7500miles?
5.) But since the seafoam did not work...if you know your egr port inside the intake manifold has never been cleaned (there is a difference in changing an egr valve and cleaning an egr port!)...then I would recommend you do that also (since the V6 is notorious for the port to be built up with carbon, mine had at least 2inch of hard carbon buildup that could only be drilled out)...do a search in the forums on here you will find out how to do it...its not hard).

For what you described one of the things listed above should fix the problem accept I am just trying to figure out why it only happens after being heated up for a while.