Shifting problem with 99 Mustang V6

I am having a shifting problem with my mustang. A while ago my engine light went off and it disappeared in 2 days before i could get some one to check it. My car started to shift into 2nd gear in less time than it
use to. And couple of days ago it started the opposite. It will take some good time to shift from 1st to 2nd gear. But rest seems to be fine. Also if i accelerate steadily, it works fine and shift normal in 2nd -5th but if i accelerate fast, it would just increase the RPM and won't accelerate.
-When its shifting.. its smooth doesn't look like its forcing into the next shift. -The Engine light is gone now. -I had an error in oxygen sensor a while ago which was something like delay in communicating with port A or C or something like that when I hooked up the code reader from my friend.
Any one knows what can be the problem. Is it a bad sensor or bad transmission??
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snipped-for-privacy@gmail.com wrote:

Have the codes read out... and look closely for problems with cruise and speedo at low speed.
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On 31 Oct 2006 00:15:14 -0800, snipped-for-privacy@gmail.com wrote:

You need to have the codes read. Keep in mind that just because the light went out does not mean the system healed itself. That is an indication of a non-critical failure. That does not mean it is not important and has no effect on the system or to drive as long as you like before getting it checked. The fault code exist whether or not the actual failure that set the code is constant. A constant light means you have a failed non-functional fault somewhere that need immediate attention and the system may be in "limp" mode to protect the system. Either way, it needs to be corrected ASAP as it will usually only get worse costing you more money and polluting the air if left unattended. In many states, auto parts stores can read the codes for free. Make sure you get the exact code if you post back here. I understand some states do not allow this practice for some reason.
Lugnut
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