1993 Lumina 3.1 low idle when warm

My 1993 Lumina 3.1 idles really low after warming up. It does not stall and drives fine up to 55MPH where it will shutter until I ease off the gas. Runs fine when cold at all speeds. A year ago I had new ECM, ICM and fuel injectors put in. Just started a couple days ago after I drove it during a heavy rain. Any ideas?

After sitting for four hours in 32F weather car still idles low. After sitting all night car is fine until it warms up.

what exactly do u mean idles low? as far as the shuddering, i assume youve checked the fluids? check the vac line coming from the regulator to the intake. remove it and see if theres presence of fluid int the line, if there is simply change the vac regulator on the trans. its on the drivers side towrards the top of the bell housing.