GM-GMC: 4.3 l gmc sonoma motor, gmc sonoma, ake

Question
the motor  start good an run idle at 600 rpm when i give alitle gas to ake it run at 800 the motor starte to shake when i rev it more it stop yet the rpm needle going from 2000 to 1900 all the time could you tell me what his wrong

Answer
The description that you have given me I find a little confusing.  What I think you are describing is a misfire that is most noticable just off idle and seems to smooth out at mid range rpm.  If what I am describing is correct you will need to locate the cause of your misfire.  I would check your cap and rotor then your plugs and wires.  Again, this is based on the description you gave which I am having a hard time understanding.
Hope this helps.