Power steering was an option on the 4 banger 97-99, wasn't standard until 2000.
As mentioned, check your tie rod ends. Also check for play in your ball joints and each end of the track bar. Other possibilities include worn universals in the steering shaft, loose steering box mount bolts and cracks/flexing of the frame where the steering components attach.
Something else to consider is your replacement steering box... it isn't perchance a rebuilt "lifetime warranty" unit from the local parts store is it? If so, they tend to not have the best reputation for being in better shape than the part they're replacing.
