Shifts into gear roughly

Make sure that your axles aren't broken. If you have a broken axle the power would transfer to the wheel with the least amount of resistance (to the broken axle) therefore not propelling the vehicle. Also look at your fluid level and condition. It is possible that the transmission is slipping in which case you'd need a transmission/rebuild.

Is the check engine light on ?
You may have a problem with a solenoid or pressure problem in the transaxle.

Start with the simple thing TRY changing out the fuel filter.

Sounds like a vacuum line. There is a vacuum line that goes to the transmission to tell it when to shift. If it has a PCM, I would suspect that because it tells the transmission when to shift to the next gear. But if you smell gas, you might have a vacuum problem.

well if you have a lot of millage it could only be the gearpump in the transy thats finished,unfotuntly ...you cant really change -it without rebuilding the all transy
other than that you still can drive-it but try letting the gear go on by it self ,you could damage your van by doing that !! you mignt not have choice but if you do ...try not doing-it!

YOU EITHER HAVE A COIL DRIVER CIRCUIT WIRE SHORTED OR FAULTY ENGINE CONTROLLER(PCM)..CHECK NEAR TRANS DIPSTICK FOR ANY DAMAGED/MISROUTED WIRING..HAVE SEEN IGNITION COIL DRIVER CIRCUIT PROBLEMS WITH PCM'S IN THESE VEHICLES ALSO

every vehicle should have one. trace your fuel line. could also be some water in your gas tank. put in some isopropol alcohol / gas line antifreeze to dissapate water.

When is the last time she had a tune up?
I would start there. Plugs, Wires, Distributor Cap and Rotor. Hope this helps you and thank you for using FixYa!