Trackpad not fully functioning after Yosemite upgrade

Question

I have a mid-2011 iMac 27".  I was running Lion and upgraded to Yosemite.  I have 12 gb of RAM and plenty of storage.
Since the upgrade, the trackpad no longer fully functions.  It will two finger swipe up and down within a window (although even that has crashed in Firefox and the only way to get the swiping back is to close and reopen Firefox).
No three finger swipes or pinching to get to Launchpad.  No four finger swipeups to get to Mission Control.  No side to side swiping either. 
No pinching to zoom in or out.  Nothing...just two finger up/down swipes and single/double taps for left/right mouse functionality.
Keyboard works just fine.  I can arrow key all over the place when the trackpad crashes, but that is a pain.
I've tried everything I've read so far. 
I've turned off  WiFi as I read in one of the threads that was a fix for someone else.
I've removed the trackpad from Bluetooth, turned it off, shut down the Mac and after rebooting then reassociated the trackpad when the Bluetooth prompt comes up.  Nope, doesn't work either although others have said that works for them.
I'm frustrated as I swipe all the time and would like to retrieve that functionality.  Help!

Answer 1

Reinstalling OS X Without Erasing the Drive
Boot to the Recovery HD: Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.
Reinstalling OS X Without Erasing the Drive
Repair the Hard Drive and Permissions: Upon startup select Disk Utility from the main menu. Repair the Hard Drive and Permissions as follows.
When the recovery menu appears select Disk Utility and press the Continue button. After Disk Utility loads select the Macintosh HD entry from the the left side list.  Click on the First Aid tab, then click on the Repair Disk button. If Disk Utility reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit Disk Utility and return to the main menu.
Reinstall OS X: Select Reinstall OS X and click on the Continue button.
Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless.
Also see:
Reinstall OS X Without Erasing the Drive
Choose the version you have installed now:
OS X Yosemite- Reinstall OS X
     Note: You will need an active Internet connection. I suggest using Ethernet
                 if possible because it is three times faster than wireless.