A couple of things to find out about?

One is, are you using only one brand of IVIG? Talk to your docs about trying other brands…can’t hurt?
And by slow rates, what do you mean? It takes two hours or seven hours and for how much? Web up the brand of IVIG and read the ‘recommended dose administrations’ -it mite require come calculations from metric to real life? But it could help you tolerate the infusions better, by changing when the rates are ‘upped’ during your infusions. Pre-meds can also help to a degree, either just Benedryl or the like and/or plus Tylenol.
You mite also consider the sub-cutaneous infusions…. there has been discussion about this extensively in the CIDP forums.
OR, consider having an IV port installed – I had one put in last year, and the stuff goes in much faster [with less pain to the arms!]. I’m getting a healthy dose of ivig now with the port in half the time, and overall fewer side effects than ever!
Ultimately between the hydration and pre-meds…you mite find YOUR happy medium. First try different brands, That’s the easiest route to start with.
Please don’t give up now! Try variations and then see. So many of the other options aren’t as effective. Keep faith and hope!