mazdatweaker
+1y
You have a couple options.
1. Take the header off and put back on the stock system, which works about as well as anything, considering 85 horsepower. An automatic transmission is an additional power leech. Somebody lied to you about what the header is going to do for you.
2. Take the header off, and grind down the transmission where it contacts the header. The header was designed for a truck with a manual transmission, so you have to modify something if you are going to insist on using it.
3. You could use a brazing torch to heat up the header where it contacts the transmission and while that part is red hot, push it in some with a pry bar. Of course, you have to be careful not to burn a hole in the header, or punch a hole into it with the prybar.