Hi-
Before you start spending money-

In what way does it rock back and forth? Is it like a side to side
action that bobs your head and shoulders? Or is it more like one whole
axle that feels weak?

How many miles?

I had a 1999.5(which is the same suspension as 2001)- early model 1999
had a slightly different rear shock setup. At 75K I replaced my front
struts with the OEM from Nissan, and OEM shocks, as well as Front Sway
Bar End Links. The End Links and rear shocks I had done in one hour at
home. The Struts- I could have done, but at $30 each for labor- I
could not refuse(I hear PepBoys charges $40 each- which is still a
good price).

This cleaned up a fair amount of slop- but I still had some side
action. The 1996 to 1999 Pathy's were tough on Rear Upper and Lower
Control arm Bushings. The bushings would fuse onto the Arm and Stud,
and be real tough to remove. While you could get replacement Poly
Bushings- you had to buy the entire arm from Nissan to go stock. Upper
Arms are roughly $150 EACH, and Lower Arms are roughly $100 EACH(there
are two each). You  can buy Poly Bushings for about $75 dollars if
your shop can press them. Earlier Pathy's were tougher on these
bushings than the newer ones(the shock remount helped)- but they still
need them sooner or later).

OEM struts are about $95 each, but you can get KYB(who makes the OEM's
anyway) about 15% stiffer for less money. Sway Bar End Links were
around $35 each, and rear shock were $45 each. All from Nissan.

I don't have mine anymore= Tranny crapped out and I bought an 06
Frontier Crew Cab 4x4.

Chris