91 grand prix idle/start problems...need ideas

I have a 1991 Grand Prix/3.1 that runs good except when stopped at stop lights. It slowly looses idle and dies. It also periodically is tuff to start. All of this occurs after it has warmed up and been driven. To date I have: put on a new fuel tank, pump. & filter, pcv valve, oxygen sensor, plugs & wires & cleaned entire throttlebody and idle air sensor. It runs a whole lot better after all of this, but the idle and starting problem is really annoying. I get tired of slipping it into neutral at stop lights. Any experienced help would be great!!

um, Guys, does this sound maybe like a partially clogged cat converter?

Could be the cat but he would have other drivability issues. I suspect problem either with the fuel pressure regulator or the fuel pump relay. I would go with the regulator first especially since he has no starting issues when cold just after it gets hot.