No rack & pinion till '99. I can't say what the difference in pumps is specifically, but I do know there are different mounting brackets '96 & after. It likely is a flow (GPM) or pressure issue you are dealing with, but... if the 'kit' seller sold you parts from all the same vehicle, then it stands to reason they should match & work together fine. What all parts did the kit include? It should have the gearbox, pump, reservoir & all hoses (hi & lo pressure) & probably a different steering shaft. (PS shaft is shorter). If the part fit, belt aligns with pulley properly, & they match each other
then I'd have to say the pump was sent DOA or maybe MOA (marginal on arrival
)... Or it's possible the box is also marginal & near needing a rebuild. If it was me, having just bought a kit, I would resolve the issue with the original seller & not spend money or time trying to make what you already paid for right after the fact. IMHO
If that's not possible, there may be a way to modify the current pump for higher flow & or pressure... it's been written up on some forums to increase PS assist for large (REALLY large) tires. If you can't resolve it otherwise, I can try & find the post with the how-to in it.