first i would try a pcm relearn. disconnect the battery for 15 mins or so, then reconnect it. your car will start up and run like ****, missing and everything, but should slowly get better. let it run for ~5-10 mins til it seems to be idling well, then go drive it around gently until she regains most of her street manners, and give her some serious wide open throttle runs. this entire process will wipe your pcm's temporary learned tables, and make it re-learn the tables. hopefully it will solve your problem.
after that, check for intake leaks, and make sure your brake booster cable is hooked up. i had idle issues when i first started my car after i installed an ls6 intake, but thats cuz the brake booster line wasn't connected in the back. once that was on, she purred like a kitten

hope this helps!!