Running problem...NEED HELP

Picked up an 2001 Ls from dealer, a week later it started running like hell. Upon initial start up, the engine would stutter & loose power, barely stay running. U could depress the gas pedal all the way 2 the floor & then engine wouldnt budge just wanna stall out....
However it seems as though after it was warmed up after about 20-30 minutes it would be fine...But who can wait that long every time u wanna driver ure vehicle..
Took it 2 the dealer, mind u this is only after owning it a week...W/out exaggeration they had it for 30 days....I Was IRATE...They replaced both fuel pumps, drained the tank & replaced fuel lines, etc..I was so annoyed i told them to keep it...Had BBB involved, attorneys etc...They said they tried everything possible & couldnt find problem, were gonna have to fly in an engineer from Detroit. Amazingly i get the call stating it was fixed & the culprit was an oxygen sensor.
Drove the car for about 1 year w/ no problems & just 1 week ago it started doing the same thing....Since acting up again it has been hit or miss, some days it's fine, others i cant get it out of my gagrage.. I was thinking it may be related to the cold weather, cause when it occurred the 1st time it was winter and since the tempature has dropped severly & has been running like hell again...
Since dropping it off @ the dealer the did get a chance 2 see how it was running. But havent found the problem yet..Im getting very discouraged already, told them how this happended last year around the same time & what another Lincoln dealers findings were...Has ne one had a similar problem or have ne suggestions...Thanks

Is your car a 3.0 V6 or a 3.9 V8?

It's a V6 bro...

Sorry, Im not an engine expert and can't help with this one... We have several VERY smart engine guys over at llsoc.com that might be able to help...

maybe its the gas

when i just bought mine i used regular and it started to loose power, then i changed it for premium and i felt the power back:P