Take the extension housing off of the new trans and try slipping the new yoke on to the output shaft....if it fits all the way onto the shaft there may be an issue inside the extension housing where the bush is located.
Also, if the new shaft has a O ring at the end of the splines remove it and try the slip yolk again...
The shaft should stick out 4 1/2" from back face of case to end of shaft...
Measure the length of the old shaft end to the rear face of the trans and compare to the new shaft and end of trans....
I suspect the output shaft in the new trans may be a 4 WD output shaft which from memory are about an inch or so longer....
