[Ptero]

My experience is LLR tires with max rated pressure give the biggest gains.
Oversize diameter rear tires will help with a 4:10. Lock-up occurs 2-3 mph (actual) higher.
Narrower tires will help.
Slow acceleration. Speed = just above lock-up (lock-up occurs about 45mph).
The return on aero mods diminishes with the weight and size of the vehicle (save it for your car).
Make sure your torque converter clutches aren't slipping. This disables the lock-up and throws error code P1740 TCC.
I use the dangerous practice of checking for vacuum leaks by spraying a little starting fluid around the intake manifold. If revs go up you have a problem.
This is a reliable engine but will suck gas. Not much you can do.

What you can do is have a beer. Now, take the number of people you are traveling with and multiply your mpg by that number. That is your passenger miles per gallon, which is a real number.
Have another beer. Figure out the weight of all the stuff you are hauling around and divide that by 160. Add that to the number of passengers and multiply your mpg by the result. That is your passengers and stuff miles per gallon which is not quite a real number but close.
Have another beer. Take your GVW and divide by 2. This is a sensible weight for a van using composite materials, designed in an imaginary world by BMW. Call the other half your stuff (you like hauling a couple extra tons of steel every where you go). Divide that number by 160 and add it to the other numbers, then multiply by your miles per gallon. That is your Hey I'm a steel hauler with passengers and stuff miles per gallon which is not a real number at all but all your friends with vans will think so.
Have another beer. Read the newspaper. See that article on the price of gas? Laugh. Laugh your head off.