'87 300D Tranny Questions

My recent purchase of a 300D Turbo has left me wanting. My 84 300D Turbo had some real get up and go when the turbo kicked in. I was quite impressed with it's performace as a diesel. The 87 of the same model however has none of that. When accelerating from a stop it seems to really move until I hit the upper 30s. I'm pretty sure it's 3rd gear because everytime it shifts the rear differential sounds like it hit the ground, but I'll save that for another post. The real problem is that between 40 and 60 there's almost no acceleration, even if I floor it to drop the gear. The RPMs just go higher and higher and when I pop back out it's back to the slow slow acceleration. Once I reach 55-60 I seem to get it back and I can get around pretty easily. This wouldn't be as much of a problem but my new job requires me to drive around all day long and it bugs me. I know there are alot of Tranny questions floating around on this forum, but I couldn't find something specifically like this. Thanks in advance.

P.S. What range should my RPMs stay in and when should I back it off?
Also does anyone know of good service manual for the 87 300D Turbo that's as good or better than Haynes. Haynes had one for my 84 but not the 87.

check the vacuum lines out of your intake maifold for cracks or rotted rubber. Mine was the same way when I bought it.