They do! They just don't put it on the trucks they sell us. The part number for the F-150 factory (OEM) XMSN pan with a drain plug is:
You should be able to find one online for about $53.00. Some guys with welders available install their own bungs and plugs cheaper. Other guys opt for after market pans. Sorry for the late reply... I used the same amount with my pan-drop fluid change, and put on the "drain plug pan" at the same time.
I read somewhere the drain plug pans were only installed on fleet orders like U-haul or some such. If a manufacturer ever wants my opinion... If it holds fluid it should have [accessable] drain & fill plugs.
93,000 miles on the clock. Interesting. Why would changing it cause it to start slipping?
I'm no mechanic but have been told by tranny mechanics that it can cause them to slip if they haven't had a fluid/filter change in a long time (miles). Guessing the dirty fluid has particules in it to help the clutches hold and clean fluid would not. Call a tranny shop and ask them. That's what I did and he told me to NOT change mine and if it started have issues then bring it in early before there is much damage.