Have a 94 Olds Bravada with 210K, we just had to replace the injectors, nut kit, spark plugs, wires, distributer cap, rotor, and oil. The car has improved so much from what it was getting (was getting 6mpg... so bad), its getting about 14mpg and runs with no black smoke anymore. When we went into the intake we tried to clean it as best as possible but it was pretty bad.

My question is it still seems off a bit, at low rpms it is rough like it might be missing. But at higher RPMs it seems to smooths out and but when you let off it seems to maybe miss. What could be causing this??

The ERG valve seemed to be pretty dirty when we took of the intake so could that be it?
(and there are no codes being thrown)

Thanks
(huge GM nut)