I'm not sure those figures are right. I plugged them in to my calculator ©
And got 248,219ft if you don't take variations in G into account and 250,776ft if you do.
Now, it could be that my calculator is still wrong, but if you use these figures:
1878mph and 229,738ft - which is the point at which Zero G occurs, and thus is when I believe all engines must have shut off,
then my calculator gives you 352,310ft for apogee, which is pretty much spot on