Is there a plug on the bellhousing on the bottom side of a 1994 Ford F150.

Seems like you have a few separate issues. A spongy brake could be a blown line, bad master and a few other things. The truck not getting up to 40 could be a couple of dozens of things and a fluid leak could be anything. You need a complete inspection here. Use this link to find a good shop near you. https://repairpal.com/repair-shops Alex