Why does my van have a burning smell when I go up hills?

Your van has a 4G60 series(62/63/64) engine, and is now 25 years old. Loss of power can be caused by many things at this age. Most likely is worn valve stems, leaking valves, and loss of compression. Could be a failing head gasket. The first step is do dry and wet compression test, then a leak down test. If there is a lot of blue exhaust smoke, the engine is burning oil (worn head or/and piston rings). If there's white smoke, its burning coolant, and you have a blown head gasket.

Assuming the rest of the van is adequately mechanically sound, the best approach is likely rebuilding the engine with new rings, possibly rebore for oversize pistons, and a re-manufactured head.

Burning to much fuel. You can do a cylinder contribution test(takes a scanner) And see which cylinder/s are lagging. Then go after the injectors. One or more could be stuck open, pouring fuel into the cylinder.

engine check lights only come n they dont say vacuum leak,you have a blown head gasket

I can answer some of your questions without being there in person.
The smell inside the van is from fresh air entering the venting system. Not sure why you don't get it from all vents. The fresh air intake is in front of the windshield and will pick up any smells from the engine compartment.
Loosing the serpentine belt would not necessarily cause you to loose ps fluid, but having a leak could drain the pump and damage the bearings in the pump, causing the pump pulley to drag on the belt.
The ps pump could be in the final stage of failing.
And the shaft seal in the pump could be leaking fluid onto the engine and exhaust.

This sounds like an oil leak. Look for leaks at valve covers, and other areas above the exhaust. It often is the burning off of this small volume of oil, that makes the smell like you describe. Inspect the whole exhaust...Something is melting, somewhere.

Could be a clogged heater core or stuck inline heater valve. Did you have the system flushed?

well 3.8 engine is not suppose to burn much gas.check for low tire pressure.if engine got many miles on it it will burn more gas,if you live in city making short stops burn more gas,if you driving a lot of roads with steep hills and mountains car will burn more gas.lead foot quick acceleration speed driving burn lots of gas.

My guess would be the vehicle is running very rich, dumping too much fuel. I would check for injectors that are leaking. Does the van have the 3.0L mitsu engine?

First you need to determine if the van is "burning" oil or "leaking" oil. If the exhaust is bluish in color, this is a good indicator that you are burning oil and you probably need a valve job. A common issue with vehicles this age is an oil leak around the valve cover gasket. Oil leaks and burns off on the manifold. If when you open the hood and smell a great deal of oil, this is more likely the cause of using so much oil. The best way is to inspect the engine compartment first. If you can't spot any excess oil there, get under the van and look for a leak near the oil pan, oil plug, or more forward toward the engine compartment. Hope you find this answer helpful. Best of luck.
Greg

sounds to me like you could have a plugged catalatic converter .