how do i remove and test the oil pressure sending unit on the 4.3 l auto transmission with a/c. i think the needle on the dash is just flipping back and forth rapidly like there is something wrong with the guage in the dash.. do not want to replace gauge inside dash as i have had this area apart before and it is very difficult to get all of the a/c controls hooked back up....is there a special tool required to remove the sending unit or just a tool that i need to purchase such as an open end wrench.????