Eratic idle

My 2000 5.7l k3500 has an idle issue. It starts and runs fine until the engine is warm. Then the idle is eratic. It seems worse when the truck is in gear. I shift to neutral and it seems to smooth right out. The problem seems to be magnified in reverse. I can hardly keep the thing running while backing up. So far no codes. I have cleaned out the IAC passages and no difference. I tried to clean the the TB with the proper cleaner but the truck will not run with the air box off. Should i take it in and get the fuel system cleaned? Any help on this problem will be greatly appreciated.

Is it only at idle? Any roughness while accelerating on the road? My first guess was bad spark plug wires, or a bad spark plug, but you should notice it off idle under some load too.

Thanks for the response. If i let it idle rough at a stop light it will run a little rough under load on acceleration, but if i shift to neutral then to drive when the light changes its fine. I have replaced the plugs and wires with delco parts. Could it be that the egr valve is not working properly? Or maybe the maf sensor?
Thanks again
Mark

Is that like Eric Idle?

My truck did this and it was a clogged fuel filter/fuel pressure regulator. May want to check that too.

Thanks i'll change the fuel presseure reg and filter. Hopefully that makes a difference.
Thanks again
Mark