Drive Shaft Problems

I have a 99 Ford Ranger. I had recently replaced the U-Joints which, was mandatory, since the avoidence of that ended tearing up my transmission tail housing.

Now I repaird the transmission, (took it to a mechanic to make sure nothing inside was screwed up) got and instaled the tail housing replaced the U-joints and driveshaft yoke.

The problem is...the yoke will only slide in half way into the transmission. I needs 1-1/2 in. more. Should I whack it with a hammer and force it in? Will it screw up anything inside?

Don't whack it with anything. I suspect that somewhere along the line, your mechanic installed the wrong part or component, either the wrong transmission tail, wrong drive shaft or wrong universal joint, more than likely the wrong transmission tail.