76 20R carb problems

i recently rebuilt my engine and the truck has been running great but slowly loosing torque, and randomly has a problem with hesation and dieing out. i have done a full tune up and valve adjustment which made little differnce. i believe i may have some vacumm issues because i havent been able to get any USEFUL diagrams on the vacumm system. also i have been trying to trouble shoot some possible carb problems but i have very little experience with carbs and am also having trouble finding some good visual aids and instructions. If you have any ideas or suggestions im open to them and would greatly appreciate it.
thanks, theodo

Finding a vac diagram for a 76 will be hard.
Auto Zone (or Advance Auto?) have diagrams on-line, but I don't know if they go back that far.

Hi. I've got a 78 with the 20R engine with similar problems. Did you ever resolve yours? Please inform.