I just double checked by putting it in 2, it shifts so that’s more proof that it does start in first. However, I have driven only 2nd gens since I was 14, so I’m pretty sure I know what first feels like. Not to mention, this truck was this slow since before the pcm swap so that wouldn’t be the issue

 

If you really want to fix it, depending on how fast you want to run, it needs 4.56 -5.13 gears to run 37s. Maybe even lower if you want power and don't care about running fast. I'm putting 4.88s in my Ford Excursion on 35s.