When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
You have a 4R100, not the 5R110 Torqshift. There is an article up in the Articles section. You can use Mercon if you can find it or Mercon V.
FWIW, it doesn't matter if you check the level in Park or Neutral. It's all the same to the tranny with the exception of the parking pawl being engaged in Park.
It's advised when using the valve body and a tuner that you should keep the tranny in stock tune and let the tuner just adjust the engine. You're doing that, right?