This kind of reminds me of mine which is a 92 chevy with a rebuilt 4.3
Upon tear down to get the rebuild process going, I stupidly threw the original EGR valve away. When I bought one when the engine was ready to go back in, I realized the new valve came with a washer restrictor kit that your supposed to match up with the original sized valve, but I had also did a exhaust mod so it was more free flowing so I took a stab at it what size washer to use. After all was said and done, the truck ran like crap. It kept kicking on the code that indicates the MAP sensor was bad. After replacing it with no change, I started disconnecting stuff hoping I could isolate where the problem was. I unplugged the EGR and capped the line. Afterwards it ran great and the MAP sensor code was gone. Ever since then I`ve left it like that. The only time it gets a code now is EGR failure every now and then.