If 75w140 won’t hurt anything but a slight mpg decrease then I think I’d prefer to keep using it as I’ve noticed the the clunk I experience when accelerating after coasting is greatly reduced with the thicker diff fluid. It very well may be placebo but I’ll consider going back to 75w90 when I remove the diff cover at 60k miles. My next project is doing a drain and fill for the ATF fluid but I’m trying to find a trans pan that has a drain plug so I can do drain and fills easier. ATF fluid is cheap enough for me to want to do a drain and fills every 30k miles. Also looking for a diff cover for the super 8.8 diff that has a drain plug.
Been there, done that. Here's my takeaway:
Dorman makes a stock style, stamped pan with a drain plug in the bottom. I worried the tack welded fitting might come loose or leak. Its about $30 at Advance Auto Parts with an online code.
A few boutique brands have thick cast aluminum pans with greater capacity and drain plugs. Reviews are more mixed than I care for on what's really just an overbuilt cookie sheet. They are usually $300+.
I've drain and filled my F150 3x over last 40k in an effort to gradually refresh the most of the fluid in my 145k mile truck. Never had any trans related issues, just a maintenance thing for me.
After dropping the pan the first time (to inspect and clean) it was obvious, in my case, that
dropping the pan more than once every few years would be superfluous. Nothing to see there.
This is what I've settled on and maybe it will give you somewhere to start. I use a $12 syphon pump with fairly tough rubber hoses, a foot of 1/4-3/8 ID aluminum or copper tubing and 6" of plastic tubing. The copper tubing get bent to your preference, connects the rubber syphon hose to the plastic tubing and protects the contraption from the heat of the catalytic convertors. The plastic tubing goes about 5-6" into the dip stick/plug. Pump ATF out into a quarts or liters graduated bucket so you have some idea how much new fluid to put back in. Swap hoses/ends on syphon pump and put same amount of fresh fluid back in.
Check fluid level according to manufacturer recommendations. Add/remove as necessary using the pump.
The rear gear covers are sexy. I had one on the Excursion. Actually, it came with it when I bought it from previous owner. Way easier to service than regular dif covers. I only used it once in 100k miles. If I could score one on eBay cheap enough I'd get another but I don't see them being worth the retail cost. You can buy A LOT of RTV for $100. Lol.