I have a 72 camaro with a TH400 with a full manual valve body with tranny brake.The pattern is P-R-N-1-2-3. My problem is when I pull the shifter to 1 it goes to 3rd. Rev. works fine and 3rd. works great also but when I try to down shift it stays in high gear or when I try to start of in 1st it stays in 3rd. I have changed filter and fluid but no change. Any help would be great because I am lost.Thanks