hard acceleration hesitation after intake gasket job

[dan fitz]

inherited a 2003 century from the mother in law and decided to do the dreaded intake manifold replacement, went well with felpro kit ( although the new bolt kit had short bolts that were not long enough so i reused the old ones). only had one bolt left over !?!? but have no idea where it came from- all the critical ones went back in properly. rather than coolant in the oil, i had oil in the coolant, which i am flushing out. first long test drive had the engine doing fine, 85 mph even going slightly uphill but when i pushed harder on the pedal it started to get weird- kind of a hesitation that sounded almost like the transmission tried to downshift but couldn't get into a lower gear or something. a/c on or off didn't make a difference. does this car have some kind of learning mode that i need to engage after the battery has been disconnected for a while? it seemed to get a little better by the end of the trip but that may be my imagination. new iridium plugs were part of the job, and it has about 80K miles on it.