The car runs and drives fine. The only problem that I am having is when you first start off from a stop. If you drive it like a grandma then you will be fine, but if you put your foot down, it start to go but at 3700 RPM's it starts to act like you are at the rev limit and wont shift until you take your foot off the gas and slow put your foot back down. Once it is third and you step on it, it down shifts and goes without a problem. Just first gear has the problem. Also, when you put the sector in Low or Drive, not overdrive, it doesn't change form Overdrive, it still shifts and drives like you are in Overdrive.

 

and your car is what and the year it was made is????? kinda hard to help with issues with no info to know how to fix...

 

Change the Transmission Filter --
Drop the transmission pan, clean the magnet that's inside, change the transmission filter, and add new fluid.
Use Motorcraft Transmission filter ONLY !! -- Original gasket is re-usable.
Your Mercury transmission requires MERCON V fluid.

Overdrive Transmission --
Overdrive engagement is NOT controlled by the Shift Lever.
Default position for overdrive is ON -- Overdrive engaged, 4 forward speeds.
To shift OUT of overdrive, press the button on the end of the shift lever.
Dash light will come on, indicating that overdrive is OFF, 3 forward speeds.