1999 suburban 440 code

I replaced my intake gaskets, replaced plugs and wires and replaced the battery all in one weekend. Everything was fine for two weeks. My check engine light came on and I had it scanned. The code came up as a 440 which the first thing you replace is your gas cap. I did that and everything seemed ok until a week later when it came on again. I bought my own scanner and it says 440. Then next thing is some kind of a purge solenoid. I did notice after all the repairs that my suburban does not make that stupid sound when you shut if off or start it up. Does anyone have an idea of maybe what controls the purging and maybe something to check to see what would be causing the code 440 to come on? :banghead:
Thanks

Since you didn't mention what motor you have, consider this a generic thing. I'll bypass the fuel cap since you've changed it.
1). Missing or damaged O-rings on the lines going to the EVAP canister.
2). cracked or punctured EVAP canister.
3). Damaged or disconnected source vacuum line, EVAP purge line, vent hose or fuel tank vapor line.
4). Incorrectly routed or defective EVAP system vacuum and vapor lines.

Conditions for setting P0440. "The EVAP system is unable to generate a vacuum greater than a calibrated value over a specified period of time".

This all out of a '98 Second Edition C/K manual.