Gas mileage is not this thing's strong point. It's mostly a short-trip-mobile grocery-getter. In that sort of driving, it gets about 15-17MPG. It has done worse. This (and horsepower-to-weight) were my objections to getting the LWB van, but my wife wanted the extra space, and it worked out to be the same price, so I went along with it.
I try to get it out and really get it thoroughly heated up at least once or twice a week to stave off sludging and corrosion issues, but mostly my wife drives it, and fairly gently; probably most of the shifts are well below 3K RPM.
On highway trips, which are mostly through northern MI over several-hundred-mile distances, it does 21-22MPG, which is a few MPG worse than the '95 got on the same trip. If it was driven a bit closer to the speed limit, there might be a 1-2MPG improvement.
Really, the thing that gets 'em is heat, from what I've read. It destroys the transmission fluid in short order, and then you get into wear issues quickly. So if the fluid and filter is being regularly maintained, you should get a lot of miles out of it.
Mine was a 3-speed automatic, and I relied a bit too much on its reputation for reliability and didn't maintain the fluid. By the time I discovered the error of my ways (after it stopped shifting properly), the trans pan was filled with thick, metallic sludge, and not a lot in the way of fluid.
Needless to say, it was over with at that point.
Incidently, all of these seem to rust in the same places: starting on the underside of the doors at the pinch-weld, especially the passenger side and slider. They also tend to rust around the rear window, although mine hadn't started to yet. I was going to swap the doors out next spring if the trans hadn't gone; I was even keeping an eye out for the forest green-colored ones to match.
Glad to hear all you had was a bad sending unit. Keep a close eye for coolant loss/leaks, that's the telltale sign that there's headgasket problems looming.
--Geoff