While it may not be built off the SAME EXACT LINE, it is probably built right next to the Hp49G+ with the SAME EXACT manufacturering processes and nearly identical parts.
If you really have to have RPN and a graphics, but don't need the fancy CAS or fast response, you should consider an Hp48G (if you have $$$$, the G+ or GX actually have more RAM than the 48GII), which still sell fairly cheaply on ebay. Nice keyboard, actually easier keyboard layout for general number crunching, built in eq Lib, very close behavior and programming to your Hp48GII.
Cons: Slow, Slow, and no CAS, and limitied memory ie holds one decent program plus 20 (10-20 steps/lines ea.) or so custom small programs (a GX could hold 3-5 decent programs plus 50+ custom programs or even more if you purchase memory cards). I use one at my desk. For general number crunching and its units conversions and eq library make it both a reference and an all purpose tool.
I have a 49G+ and find its speed very easy to get used to. For work though I cannot afford to miss keystrokes, but for fancy coursework, I might give it a chance. But I just don't trust it to hold up at work. Therefore, I don't beat on it nearly as much as my tried and true Hp48G (I actually have a GX at home also, but I find the garbage collection on the GX with its extra memory to take longer and therefore seem even slower than the lower end HP48G). Therefore for general use, the Hp48G actually seems much faster than the Hp48GX.
My advice: Send it back for replacement (actually you might get Hp to replace it with an Hp48G+ if you ask). But the performance of the Hp48G+ may not be acceptable to you either.
But you might also consider buying an Hp48G on ebay, typical price is $30-45.