So one of the first mods I did was removing the monstrous 3-point towing mirrors. It was unbelievably loud when I first started driving it on the highway, and I could barely go 70mph, while drafting, at full throttle....downhill. I couldn't keep up with highway traffic unless I lucked out and found a truck to draft. I yanked the passenger mirror and installed a bullet-style camera. I have a backup blind spot mirror inside the door, and wired the camera to a cheap Pyle 8" LCD monitor that I picked up off of fleBay. This drastically reduced the wind noise.
I scored an OEM Ford paddle-style driver's mirror from a 2003+ E150, and drilled a couple of new holes to mount it. It's the same shape as the 1990s mirror mount area, just 2 holes don't line up. These two changes did not improve my mpg, because instead of struggling to keep up with traffic I was suddenly able to drive 70-80mph without being at full throttle or going deaf.