Rear shocks (van 150000 miles) originals still on Recently installed 2.2 Legacy Engine people sugges KYB gas shocks I have Biltiens *new) on front

https://www.manualowl.com/am/Oldsmobile/1995-Silhouette/Download/972
(page #3-4 to 3-6)

check the vans rear shock absorbers if they are faulty the car can exhibit this type of behaviour and braking will be less efficient. Also tyre wear will be affected to.
I am not a shock absorber expert but had recently my four shock absorbers replaced as the fluid had ruptured in the front shockers and the rear mounts for the rear shockers were corroded and unsafe. (shock absorber expert at repair place mentioned the symptoms you are describing as a rear shock problem or the rear leaf springs are faulty)

Ignition Wires on wrong

Worn out Cats --can't test?
140,000 miles & 11 years--replace them

Check Fuel pressure

Front O2 Sensors--not the issue, but get
changed at 100,000 miles

What the back is to low or left and right side not even if you whant to lift the rear suspension air shocks

The struts model (MacPherson Strut),are both in front and back of this car.
2000 - 2006 Hyundai Elantra Shock Absorber and Strut Assembly - Rear, Driver Side, KYB GR-2/EXCEL-G, Twin tube, Strut Assembly. $72
2000 - 2006 Hyundai Elantra Shock Absorber and Strut Assembly - Rear, Passenger Side, KYB GR-2/EXCEL-G, Twin tube, Strut Assembly $68
1996 - 2006 Hyundai Elantra Shock Absorber and Strut Assembly - Front, Driver Side, KYB GR-2/EXCEL-G, Twin tube, Strut Assembly $67
1996 - 2006 Hyundai Elantra Shock Absorber and Strut Assembly - Front, Passenger Side, KYB GR-2/EXCEL-G, Twin tube, Strut Assembly $63
Of course this is only the cartridge, you have to transfer the spring, and the top mount of the existing strut. You need a pair of coil spring compressor to do the job. The basic procedure to replace a strut is:
Remove the top nuts that secure the strut assembly to the frame mount inside the engine compartment. Do not remove the center nut.
Mark the lower strut mounting location on the hub for installation reference. The alignment will be close if the new strut is installed in the same position.
Remove the bolts that hold the strut assembly to the hub.
Remove the strut assembly from the vehicle.
Mark the top mount for installation reference. Using a side mounted spring compressor, compress the spring and remove the top nut and retaining washer. Pull strut assembly out from the bottom of spring.
Slide the new strut assembly up into the spring and reposition the top mount onto the spring in the same position that it was removed. Install the retaining washer and top nut.
Tighten the top nut to the manufacturer's specifications and carefully remove the spring compressor.
Place the strut assembly back into the vehicle.

at 150,000 miles pretty much everything could be worn out if it is all original, if the van is in really good shape no dents or bad dings paint good, interior is in really good shape and the van has been serviced on a regular basis then yes fix it, also this is a free wheeling engine so if the timing belt breaks there is no damage to the engine, if it ran good with no excess oil useage or engine noise fix it..

Do you feel it at slow speed, like in the parking lot? If so, its a tire or wheel issue. At slow speed if the steering wheel wobbles, its in the front, if you feel it in your ****, its the rear. If its at high speed 40-50 it may be a balnce issue, have a shop that does a lot of tire work check it, stay out of chain stores. This should not be hard to find.

Both of the following manufacturers produce decent shock absorber./strut assembly units for the front and rear of 2002 Lancer models.

1. KYB; and
2. MONROE

Cheers
Sean Voluntary contributor.

Before you upgrade parts like a rear sway, how many miles on the vehicle?
Have the shocks and struts ever been replaced?
What is the condition of the existing sway bar bushings?

If these parts haven't been replaced recently, I would start there. You can also upgrade these parts with better components then stock (like gas shocks, upgrade bushings etc).

Also air pressure in your tires. Just being a couple of pounds off can effect the handling of a vehicle, same goes for condition of the tires, and even what brand of tire you use.