Car shakes after starting up.
I have a 1993 Nissan Altima Gxe

I did an oil change on 9-14-07
Then I filled up gas on Saturday 9-15-07.

The shaking started after I filled the gas up.

The Oil change place I took it took does have some bad reports online.
This particular place has a trust worthy mechanic and is high
respectably  in this community.  This person would go out of they way
to help you.   He was there at the time of the oil change,   No oil
leak.  

It shakes real bad.    
What is odd about the shaking?  It seems to be worse under 30 miles
and hour.   Less shaking above the 30 mph. I noticed it shakes a lot
worse with the overdrive on.  I had to turn it off.  To even go.

I took it back to the place.  He told me I could of got air or bad gas
in the tank.     He told me to drive it awhile and it could clear up.

My questions.
Should I drive it until I get the gas when it gets down to 1/2 tank or
even 3/4 of a tank?  Then add gas.  I got the gas at Sunoco 91 grade.
Which usually does great.

Should I add a gas treatment to Nissan.?  What brand should I use?
The last time I did a treatment.  I had to replace a distributor cap.
It is a fuel injection engine

Should I take it to a shop or is there another cause?
Spark plugs and wires look ok.

Thank You,

Greg Rozelle
P.S.  I know there is a debate with leaving the overdrive on or off or
only turn it on at a certain speed.

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