Hey im new here, i have a 1988 K5 Blazer tbi (i know not gmt400 but you guys know a lot about tbi) Ive been having this issue where the truck will run super rich causing it to be very sluggish and guzzle gas. There is no smoke out the tailpipe but i went from averaging over 15 down to getting under 5mpg. Ive replaced the o2, cts and connector, map connector, iac and connector, tps connector and tested tps to verify is correct, rebuild throttle body, new fuel pump reg. and filter, new air cleaner, cleaned both grounds on top of manifold, new egr, almost everything. The truck also has developed a rough high idle and jumps from 700-800rpm then drops to jumping 600-700rpm. Please help Im lost here.