tre5
+1y
I'm not sure the differences in size between the manual trans and the auto trans, but if you go 2.5", you will need to do a small amount of clearancing for the trans (with the auto). You can do a couple tricks to minimize the cuts in the floor though. When you build your new frame, move the body mounts rearward .5"-.75". This will essentially move your engine and trans forward, along with your front suspension (which will better center the wheel in the wheel well when laid out.) Another place this will help is the size of the firewall tubs. The final benefit do doing this when performing the stock floor is it will close up the gap between the bed and cab. If you find you still need to clearance the trans tunnel, you can move the engine and trans forward a bit more by relocating the engine mounts on the frame. Good luck!