I've got the same vehicle and engine but fortunately, I don't have any performance problems with mine.
If you do any trailer towing like I do, the engine bogs down on hills as it will have reduced power thanks to the corn. I refuse to use E85 in mine.
Is there any spark arcing during the cold start time? Are the plugs/wires in good condition?
There are a number of things that can cause this problem, among them are vacuum leaks (check for intake leaks around the manifold and plenum), also the vacuum hoses.
Perhaps a bad IAC valve or maybe just a dirty throttle body.
I initially was going to mention a possible plugged fuel filter, but you said it runs good when warmed up.
PVC good? Easy to check. (any suction or does it rattle when shaken?)
Let me know how this turns out, ok?
Sorry I can't be a bit more positive as to the cure.