It sounds very much like the exact symptoms that I have in my van right now, the same year and model.
For the gas gauge, there is a 99% chance that the fuel level "sender" (sensor - in the fuel tank) has gone bad. This happens as "junk" in the gas builds up on the sensor and causes it to fail. I can give you a location of a connector that you can measure the resistance value coming from the sensor (under the van, just behind the driver's seat), if you have a multimeter. The reading should be somewhere between 40 ohms (empty) and 250 ohms (full). Anything outside that range, or if the reading "jumps around" by more than a few ohms when you rock the van, then the sensor needs to be replaced.
As for the temperature gauge, mine takes "forever" to go up too. The only time I can even get it to up to between 1/4 to 1/2 scale is when I just let then engine run while the van is not moving, such as when it is parked in the driveway, or a long trip through a drive-through. As soon as I start driving around, the temperature gauge goes back down.
The issue with that is the thermostat is stuck open. This allows the coolant to circulate all the time through the entire system (including the radiator). If I am driving, air moves through the radiator and keep the engine cool, and sometimes, too cool. This will sometimes cause a P0128 error code to be stored in the computer and the radiator fans will come on any time the engine is running. The "fix" for this issue is to replace the thermostat, which is not that easy in these vans. The factory manual calls for 2.5-3 hours to do the job.
I would not recommend that either of these jobs (replacing the fuel sender or thermostat) as a "do it yourself" job. I would take it to a shop and have it done there.
I hope this helps. Please let me know if you have more questions.
Take Care, Greg A.