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Try disconnecting your O2 sensor, and see if the acceleration stumble stops. If so, it's probably your O2 sensor.
Check out this thread for tire PSI discussion:
http://ecomodder.com/forum/showthrea...res-26464.html
Make sure you check out
100+ Hypermiling / ecodriving tips & tactics for better mpg - EcoModder.com and
65+ Vehicle modifications for better fuel economy - EcoModder.com for suggestions on increasing MPG.