After DTC clearing does the computer have to reset?

We have a 5.3 in a 2008 Avalanche LTZ,the engine light came on so I took the programmer off of it as directed by the company and sent it to the Chevy Dealer for a DTC of 455. They replaced the vapor solenoid cleared the code. The truck was getting 18 MPG city hwy combined before the dealer deal. I reinstalled the programmer and get 16 MPG. I call the dealer and the service mgr tells me the truck computer has to relearn our driving habits. I take the prgrammer back out of the truck and try driving without it. Now we're are at 14 MPG.  WTF Can anyone tell me what is going on and how to get this truck back to life. It also shifts inconsistantly and revs out of character when shifting.  

do you have a scan tool that will display live data... like the harbor freight 98614.????/ warning.. not all scan tools display live data streams... some only show snap shot data..... this one does most of what the pro units do.....

i would say....    plug in the scan tool... check for codes.....   you might want to verify that the purge valve was properly installed and operating as designed...    not just bypassed.... or broken.... as that will reduce the fuel economy...   as the engine vacuum is pulling in uncommanded fuel...


the fuel display will be the commanded fuel... so.. it could be driver technique.. or another problem..

if there is a code set...  or a problem with one of the many different sensors or system that causes the system to fall into limp home... the fuel economy will suffer... your flared shifts.. could do that without turning on the check engine light...  but still have a code set....  the transmission is controlled by the PCM also...

you might after you verify that there are NO codes stored..

find a large open road area... where you can safely .. disconnect the battery....   wait a few minutes.. reconnect the battery...  this will reset the PCM>...  then get in.. drop the transmission in drive and accelerate to 50 miles an hour... holding your foot steady on the gas pedal...  stop and do the acceleration again.. NOT LIFTING the throttle to force the transmission to shift... the PCM has to learn the shift points this way...


if you get in after having the battery disconnected... and hammer down on the throttle.. the ecm will not learn the proper shift points....    

i also worry about the flared shifts...  did anybody get in and abuse the  truck...


you might want to print this chart....   and with the scan tool examine your data stream...



you might also want to check the transmission fluid level....    swap in a new transmission filter and refill the transmission...   make sure to examine the sediment in the bottom of the pan.. a little dark fiber is ok.. but if you get brass, aluminum, steel flakes... you might have a problem...