The Manual shift problem is probably a Cable bind or adjustment problem.
The Auto shift problem sounds like the TV/ThrottleValve Cable is too tight.
Also, if you're running an aftermarket Carb, Holley, Demon or Edelbrock you need a Geometry Corrector Bracket on the Carb's linkage for the TV Cable.
Holley/Demon >> http://www.summitracing.com/parts/SUM-700202/
Eddy >> http://www.summitracing.com/parts/SUM-700203/
TV & TV Cable Info:
3-Parts >> http://www.tvmadeez.com/article/index.php
http://www.jakesperformance.com/TV_Cable_Setup_Info.html