HELP: Difficult To Start When Cold

Hope someone can help with some feedback/advice.
I have a 96 V6 Automatic that lately has difficulty starting up in the mornings or whenever it sits for a long time.
The starter will crank and the engine will turn but it wont start up till after the 3rd or 4th attempt. Yesterday I spent over $300.00 on a Tune Up changing the plugs the fuel filter one O2 Sensor that was showing up as too lean on Bank 1. I also replaced the Air filter and the PCV valve. The vehicle now in the 80k milage range and I have been taking good care of the car with regular maintainance. I don't want the machanics to make me spend too much on them trying to find out what is wrong so I appeal to this newsgroup for help.
Also, the mech told me that I have only 3 O2 Sensors is that right? I always thought I had 4. He also recommended I use high grade gasoling instead of the regular which I began using after getting tips from this very newsgroup some time back. Pls help me out. I appreciate any assistance given.
Thank you all in advance. Winston
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