That is interesting. I want to get a new EGR for my new engine, and I was going to get a cheap Chinese one for $35, but after your post I am re-thinking that. I found a Delphi one that is an OEM replacement, but they are $100.
I honestly can't speak as to what is different, either. If I've got my terminology right, there are two main categories, positive and negative backpressure (apparently relating to relying on vacuum or exhaust backpressure to open them up or feed EGR to the engine) but beyond that GM used a host of part numbers. You'll see the aftermarket ones listing 3+ GM numbers they replaced, and GM did not just randomly reassign part numbers. Probably akin to the vacuum pots on the Q-jets, would not be surprised if they had to be different based on the vacuum the particular engine pulled under X operating conditions, and probably a particular diameter orifice on the vacuum fitting, among other things like GVWR, axle ratio, etc.
It's pretty hard to stomach the cost of the OEM EGR valves, but at the same time, it would suck to spend $35 and have a problem remain, or change due to an incorrect EGR, which would be near impossible to know if it was the issue. And while probably often not done for any legitimate reason, cost of replacement IMO is certainly one reason to eliminate EGR. Of course, eliminating it with a carb or TBI presents their own difficulties.
For the OP, disconnect the EGR solenoid, or the vacuum hose (and plug it) and see if the problem goes away. Should trigger a CEL, but will not affect the engines performance with the light on. If the problem is gone with the valve disconnected, there is something wrong in the EGR circuit...check the hoses for condition and routing...about the only thing that could cause an issue with it running other than the valve itself. Pretty tough for the electrical side of that circuit to work just enough to screw up how it runs.
