After driving for awhile, and I get caught in traffic or a long light, my 98 mustang begins to shake a little and i can see the temp gauge start to go up. If i turn off the car and try to restart it too soon, It shakes pretty violently. If i start driving the temp goes back to normal. Any ideas?
Make sure the cooling fan(s) work properly.
For one thing it sounds like your cooling fan isn’t operating. Overheating while sitting still and cooling while driving is normally a dead giveaway.
Aside from that however, have you actually checked the coolant level?
The shaking is troubling - is your check engine light flashing at that time? Any smoke out of the exhaust? Have you actually let the temp gauge get into the red? Before you do too much to it I would have a shop evaluate it for any head gasket problems.